AIR CONDITIONING AND CLIMATE CONTROL
Course 752
©2004 Toyota Motor Sales, U.S.A., Inc.
All rights reserved. This book may not be reproduced or copied, in whole or in part by any means, without the written
permission of Toyota Motor Sales, U.S.A. Inc.
Printed in the U.S.A.
Ver. 1 – Jan. 2005
Toyota Motor Sales, U.S.A., Inc.
Course 752 Toyota Air Conditioning and Climate Control
Table of Contents
Introduction
Introduction to Toyota Air Conditioning
and Automatic Temperature Control . . . . . . . . . . . . . . . . . . . . . . . v
Section 1
Preparation
Safety Practices . . . . . . . .
Compressed Gases .
Electrical Circuits . . . .
SRS/Airbag Systems
Tools and Equipment
Section 2
The A/C System
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.........................
........................
........................
........................
........................
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1-1
1-1
1-2
1-2
1-3
The Refrigerant Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Expansion and Evaporation . . . . . . . . . . . . . . . . . . . . . .
Compression and Condensation . . . . . . . . . . . . . . . . . .
Refrigerant Properties . . . . . . . . . . . . . . . . . . . . . . . . . . .
Basic A/C System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
2-1
2-1
2-1
2-1
2-2
2-3
2-4
Section 3
A/C System
Components
Expansion Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Evaporator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Expansion Valve/Evaporator Interaction . . . . . . . . . . . . . . . . . . . 3-4
Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Compressor Clutch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11
Condenser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
Receiver-Drier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14
Pressure Relief Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16
Multipressure Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-17
Lines and Hoses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17
Cooling Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
A/C Blower Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22
Review of Refrigeration Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . 3-23
Section 4
Diagnosis and
Repair
Systematic Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1
Toyota Six-Step Diagnosis Process . . . . . . . . . . . . . . . . . . . 4-1
System Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Need for Periodic Maintenance . . . . . . . . . . . . . . . . . . . . . . .4-3
A/C-Specific Maintenance and Inspection . . . . . . . . . . . . . .4-3
Diagnostic Trouble Codes (DTCs) . . . . . . . . . . . . . . . . . . . . .4-4
Special Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
Recovery-Recycling-Recharging Station . . . . . . . . . . . . . . . .4-7
Leak Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-7
Leak-Testing Dyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-9
System Sealant (“Stop Leak”) Products . . . . . . . . . . . . . . . .4-9
Refrigerant Identifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-10
Drive Belt Tension Gauge . . . . . . . . . . . . . . . . . . . . . . . . . .4-11
Miscellaneous Special Tools . . . . . . . . . . . . . . . . . . . . . . . .4-11
Resource Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-13
Troubleshooting, Service and Repair Tips . . . . . . . . . . . . .4-14
Component Replacement . . . . . . . . . . . . . . . . . . . . . . . . . .4-15
Refrigerant Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-16
Flushing Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-16
Evacuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-16
Refrigerant System Lubrication . . . . . . . . . . . . . . . . . . . . . .4-17
TOYOTA Air Conditioning and Climate Control – Course 752
i
Table of Contents
Adding Oil After Repairs . . . . . . . . . . . . . . . . . . . . . . . . .
Inline Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Performance Checking . . . . . . . . . . . . . . . . . . . . . . . . . .
Recovery and Recycling Techniques . . . . . . . . . . . . . . . . . . .
Equipment Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Noncondensables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage Cylinders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ii
.
.
.
.
.
.
.
.4-17
.4-18
.4-19
.4-19
.4-20
.4-20
.4-22
Section 5
A/C System
Controls
Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
Heater Control Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
Air Mix Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . 5-3
Blower Speed Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
Air Distribution Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-6
Air Inlet Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
FRESH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
RECIRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
Typical Mode Position Charts . . . . . . . . . . . . . . . . . . . . . . . .5-10
Dual-Plane Air Distribution . . . . . . . . . . . . . . . . . . . . . . . . . .5-11
Section 6
Automatic
Temperature
Control
Introduction to Automatic A/C . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
Automatic A/C Temperature Control . . . . . . . . . . . . . . . . . 6-1
Automatic A/C Components . . . . . . . . . . . . . . . . . . . . . . . . 6-3
Customized Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-4
A/C Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-5
Automatic A/C Control Panel . . . . . . . . . . . . . . . . . . . . . . . .6-7
Temperature Sensor Circuits . . . . . . . . . . . . . . . . . . . . . . . . .6-8
Servo-Motor Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-8
Control of Blend Air Damper . . . . . . . . . . . . . . . . . . . . . . . .6-10
Pressure Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-11
Belt Protection Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-12
Thermistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-14
In-Car Sensor (Thermistor) . . . . . . . . . . . . . . . . . . . . . . . . .6-14
Ambient Temperature Sensor (Thermistor) . . . . . . . . . . . .6-14
Solar Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-15
Sensor (Thermistor) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-16
Maximum Cool Damper . . . . . . . . . . . . . . . . . . . . . . . . . . .6-17
Multimode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-17
Rear Air Conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-18
Section 7
Automatic
Temperature
Control
Diagnosis and
Repair
Diagnosis of Automatic A/C Systems . . . . . . . . . . . . . . . . . . . . .7-1
Diagnosis Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
Testing Sensor Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4
Testing the Solar Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5
Testing Servo-Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6
Automatic A/C System Repair Techniques . . . . . . . . . . . . . . . . 7-7
A/C System Odors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7
Diagnosing the Automatic A/C System . . . . . . . . . . . . . . . . 7-9
TOYOTA Technical Training
Toyota Air Conditioning and Climate Control
Section 8
Air Conditioning:
Hybrid Vehicles
A/C Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
A/C Components Comparison . . . . . . . . . . . . . . . . . . . . . . .8-2
A/C Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-3
Refrigerant Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-4
Other Hybrid HVAC Components . . . . . . . . . . . . . . . . . . . . . . . . .8-4
Heater Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-4
Water Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-6
Temperature Control System . . . . . . . . . . . . . . . . . . . . . . . . .8-6
Electric Inverter A/C Compressor Control . . . . . . . . . . . . . .8-9
Room Temperature and Humidity Sensor . . . . . . . . . . . . .8-10
Hybrid System Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-11
Troubleshooting/Self-Diagnosis . . . . . . . . . . . . . . . . . . . . . .8-11
Self-Diagnosis Procedure . . . . . . . . . . . . . . . . . . . . . . . . . .8-12
Glossary
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
TOYOTA Air Conditioning and Climate Control – Course 752
iii
Table of Contents
iv
TOYOTA Technical Training
Introduction to Toyota Air Conditioning
and Climate Control
Course 752, Toyota Air Conditioning and Climate Control is a technical
training course that covers basic through advanced concepts of mobile
air-conditioning systems, and basic and automatic temperature-control
systems used on Toyota vehicles. This course will familiarize you with
the theory of operation, troubleshooting techniques and repair procedures
necessary to diagnose and repair Toyota air-conditioning systems.
The Technician Handbook presents information in a logical order for use
during the course and for reference in the shop.
A prerequisite to this course is successful completion of Course 623,
Electrical Circuit Diagnosis. You should have completed the Self-Study
Prework Modules before attending this course.
Course 752 uses this Technician Handbook, other Toyota reference
manuals, sample components, integrated worksheets and hands-on
lab activities with vehicles to broaden the air conditioning repair and
diagnosis skills of the technician.
TOYOTA Air Conditioning and Climate Control – Course 752
v
Introduction
Course
Objectives
After completing this course, you should be able to meet the following
objectives:
• Effectively diagnose and repair Toyota air-conditioning systems using
approved resources, tools and procedures
• Effectively operate Toyota-specified recovery/recycling equipment and
recharge vehicle A/C systems
• Demonstrate a working understanding of the principles of the
automatic air-conditioning system
• Successfully diagnose and repair Toyota Automatic A/C systems
Note:
Federal, state or local regulations may require technicians to receive
additional training or certification prior to working on the refrigerant
circuits of mobile air-conditioning systems. Consult the appropriate
city and state regulations for handling refrigerants and for additional
information.
Information contained in these course materials is subject to change.
Reference should be made to the Technical Information System (TIS) and
to current Toyota Vehicle Repair Manuals, Electrical Wiring Diagrams and
Technical Service Bulletins (TSB) for exact specifications and procedures.
vi
TOYOTA Technical Training
Section 1
Preparation
Lesson
Objectives
1. Demonstrate safe practices for working with compressed gases.
2. Demonstrate safe practices for working with electricity and
Supplemental Restraint Systems (SRS).
3. Identify tools and equipment necessary to diagnose and repair the
air-conditioning system.
TOYOTA Air Conditioning and Climate Control – Course 752
Section 1
Preparation
Safety
Practices
Throughout this course and during normal A/C service procedures, there
is a possibility for dangerous contact with moving parts, pressurized
gases, high current electrical circuits and accidental deployment of the
supplemental restraint system (“airbags”). Consider the potential hazards
involved and use the following safe working practices.
Compressed
Gases
Pressurized gases are present in vehicle air-conditioning systems, recovery/
recycling equipment and even manifold test gauges. All pressurized gases
exhibit two characteristics that can be hazardous:
1. When heated, internal pressure increases (rises).
2. When pressure is suddenly released, the temperature of the gas
decreases (drops).
These properties of a compressed gas can be hazardous in two ways:
1. If heat is applied to a pressurized system (bright sunlight, lack of
ventilation, use of steam cleaner or welder, etc.), system pressure can
quickly increase beyond a safe limit. This could result in an explosion
with the danger of injury from flying metal fragments.
2. If refrigerant gas rapidly escapes, there is a danger of frostbite.
Frostbite is a serious injury that results in tissue damage caused by
localized freezing and requires medical attention. Since the eyes are
made of delicate tissue, they can be damaged by direct contact with
even a small amount of escaping refrigerant. Always wear safety
goggles when working with refrigerant.
Risk of Frostbite
Warning: Refrigerant is a
compressed gas and can
burn skin or eyes.
Fig. 1-1
752f101
TOYOTA Air Conditioning and Climate Control – Course 752
1-1
Section 1
Electrical
Circuits
The low voltages used in vehicles generally pose little risk of electrical
shock. However, many repairs require using equipment powered by
120 volts with high current. Accidental short circuits can damage
components or test equipment. Touching a wire that is shorted to ground
can burn you. Observe the following to reduce the risk of personal injury:
1. Verify all 120-volt equipment line cords are in good condition and
properly grounded.
2. Before making resistance measurements with an ohmmeter, first
confirm the circuit source voltage is OFF by testing the circuit with
a meter set to measure voltage.
3. When bypassing components to test a circuit, use a fused jumper wire
to protect against accidental short circuits.
SRS/Airbag
Systems
The Supplemental Restraint Systems (SRS) are designed to deploy only
in response to a significant frontal or side impact. To prevent accidental
deployment, disconnect the ground (negative) cable from the battery and
wait for up to 60 seconds before performing any repairs which involve
disconnecting any SRS wiring. SRS-related circuits are identified by bright
yellow wire harnesses and connectors.
Before disconnecting the battery cable, make a note of the radio presets,
Auto A/C panel settings and the display of any system fault codes.
Precautions
for Airbags
• Read all precautions
in the Repair Manual
prior to work.
Fig. 1-2
752f102
1-2
TOYOTA Technical Training
Preparation
Tools and
Equipment
Accurate diagnosis and efficient repair depend on using the correct tools
and information. In addition to Vehicle Repair Manuals, Electrical Wiring
Diagrams, Technical Service Bulletins and a standard technician’s tool set,
the following Special Service Tools and other equipment may be needed:
Recommended Tools (or equivalent)
Part Number
A/C Recovery/Charge Station
Refrigerant Identifier
Refrigerant Leak Detector
Thermometer Dial Type — 0 – 220 degrees F
DVOM Meter
Dial Indicator with Magnetic Base
Cooling System Pressure Tester
Condenser Fin Straightener
R-134a Valve Core Removers
Magnetic Clutch Remover (SST)
07112-66040
Magnetic Clutch Stopper (SST)
07112-76060
A/C Quick Joint Puller #1 Suction Tube (SST)
09870-00015
A/C Quick Joint Puller #2 Liquid Tube (SST)
09870-00025
Toyota/Lexus Diagnostic Tester
(SST Hand Held Tester/SCAN Tool)
01001270
Belt Tension Gauge (SST) 09216-00021
Eye Protection Goggles/Safety Glasses with Side Panels
Rubbers gloves
TOYOTA Air Conditioning and Climate Control – Course 752
1-3
Section 1
Notes
1-4
TOYOTA Technical Training
Section 2
The A/C System
Lesson
Objectives
1. Identify and demonstrate the function of the basic refrigerant circuit.
2. Identify the low- and high-pressure sides of the refrigeration circuit.
3. Identify the major components of the A/C refrigeration circuit.
TOYOTA Air Conditioning and Climate Control – Course 752
Section 2
The A/C System
The
Refrigerant
Circuit
The basic A/C system contains components to push refrigerant through
a closed system in order to extract heat out of the vehicle interior and
transfer that heat to the outside air. This cycle continues constantly until
the vehicle’s interior reaches a set temperature. Inside the A/C system,
the refrigerant changes from a liquid to a gas and then back to a liquid.
As we shall see, this “phase change” is what helps remove heat from the
air circulating inside the vehicle.
Expansion and
Evaporation
If a pressurized liquid is released into an area of lower pressure, it will
evaporate into a gas and absorb heat from that area. This is the principle
that causes the spray from an aerosol can to feel cold to your skin.
Likewise, a liquid that changes from liquid to vapor at a low temperature
(e.g. alcohol) will feel cool on the skin as it evaporates (phase change).
This is the situation you feel when you get out of a swimming pool or
shower. The evaporating water on your skin absorbs heat from your body
even though the air temperature is quite high.
Absorb Heat
Vaporization
Vaporization
(Evaporation)
Liquid
Vapor
Condensation
Reject Heat
Fig. 2-1
752f201
The device that regulates pressure in an A/C system is the expansion
valve. The area where heat transfer takes place is the evaporator
(heat exchanger).
TOYOTA Air Conditioning and Climate Control – Course 752
2-1
Section 2
Compression
and
Condensation
After the gaseous refrigerant absorbs heat, the system pressurizes it to
change it back into a liquid. As this happens, the gas gives off much of
the heat that was absorbed. This is what the compressor and condenser
do in the A/C system. In order for the gas to actually give up heat while
in the condenser (heat exchanger), it must be hotter than the air around
it. The compressor makes this possible by increasing the line pressure,
and therefore, the temperature of the refrigerant gas.
Refrigerant
Properties
Automotive air conditioning has been widely available since the 1940s.
The refrigerant CFC-12 or R-12 (also known as Freon®) was used for many
years due to its relative safety in contact with humans and its low boiling
point of –21° F. In other words, the CFC-12 refrigerant (HFC-134a –17°),
and most liquids used as refrigerants, change from a liquid to a gas at a
very low temperature.
For the last decade, another refrigerant, HFC-134a (R-134a), has been
developed for use in automobiles due to its less negative impact on the
environment. Most new vehicles manufactured today use HFC-134a.
Federal laws regulate the use, recycling and recharging of CFC-12 and
HFC-134a refrigerant.
Heat and Matter
Using water as an example, we can commonly find water in any of
three states: Ice, water and steam. Its temperature is what determines
the state of water (H20).
Three States
of Matter
212°
31°
60°
Fig. 2-2
752f202
The concept of heat is directly related to the nature of all materials. Some
materials are solid, some are liquid, and some are gaseous. In fact, all
matter can exist in each of these three states depending on its temperature.
2-2
TOYOTA Technical Training
The A/C System
Matter has different characteristics as it exists in each different state.
For example:
1. A solid has a defined shape and cannot flow to fill empty spaces in
a container.
2. A liquid can flow to fill voids in a space, but it cannot be compressed
or made more dense by pressure.
3. A gas (or vapor) also flows easily, and it can be compressed; that is,
its density can be made greater or smaller by applying pressure to a
closed vessel containing the gas.
As heat energy is applied to a solid, the solid absorbs the heat (we could
say it “gets hotter”) up to a point. If the solid is heated past its freezing
point, it will gradually become a liquid. The heat required for this to
happen is called sensible heat. As heat energy is added to a solid, its
observed temperature will increase. In fact, this relationship is consistent
for each material. However, the process of changing its state requires the
addition of an extra amount of heat.
Latent Heat is the additional energy necessary to cause refrigerant to
change state from a gas to a liquid or from a liquid back into a gas.
Water boils at 212° F and applying additional heat will not raise the water
temperature but will increase vaporization or evaporation rate resulting in
steam vapor. Humidity reduces the absorption of heat into the evaporator
coils until the moisture is condensed on the coils and fins then drained
from the case by the drain hose.
In fact, at the point at which a change of state is about to take place,
a material will absorb a significant amount of heat without getting
noticeably warmer. The additional heat is called latent heat, which
means, unnoticed heat.
TOYOTA Air Conditioning and Climate Control – Course 752
2-3
Section 2
Gas
Sensible and
Latent Heat
Liquid
100° C (212° F)
Solid
0° C (32° F)
Sensible
Heat
Latent
Heat
79.3
kcal/kg
Sensible
Heat
100
kcal/kg
Latent
Heat
539
kcal/kg
(143 BTU/lb) (180 BTU/lb) (790 BTU/lb)
Pressure and
Temperature
Fig. 2-3
752f203
A physical relationship that affects heat transfer is the effect of pressure
on the boiling point. When water freezes at 32° F (0º C) and boils at 212° F
(100° C), these values only apply with an open container at sea level
where the air pressure is 14.7 psi.
Effect of Pressure
on Boiling Point
Pressure, psi
If, for example, the altitude is 5000’ above sea level. The atmospheric
pressure is only 512.5 psi and water in an open pot will boil at only
195° F (91° C). In addition, at this altitude, water will freeze at 35° F (2° C).
In an extreme low pressure environment (sometimes called a vacuum),
the boiling point can be further reduced and the freezing point increased
until they meet. At this point, freeze-drying occurs and solid water (ice)
changes state directly into gaseous water (steam).
30
15
(Vacuum, In. Hg)
30
(7)
(15)
(22)
(30)
0
50
100
150
Boiling Point of Water, °F
2-4
TOYOTA Technical Training
200
250
Fig. 2-4
752f204
The A/C System
As pressure is increased the boiling point also increases as in a radiator
with a pressure cap. The increase is approximately three degrees of boiling
point for each one psi of pressure increase, meaning a 15 psi radiator cap
will increase boiling point by 45 degrees F.
Humidity
and A/C
Performance
Relative humidity has a great influence on the apparent cooling effectiveness
of an A/C system. The higher the humidity in the air, the less energy is
available for cooling. A side benefit is that removing humidity from the
interior air is in itself an improvement in comfort since humidity prevents
the body from dissipating heat in its normal manner.
Humidty vs.
Performance
Temperature Difference
Between Inlet and Outlet
°F
72
68
64
61
57
54
50
50
60
70
Relative Humidity (%)
Fig. 2-5
752f205
Humidity reduces evaporator heat absorption and efficiency due to
humidity condensing on the coils and draining away out the drain tube.
Different
Temperature
Scales
Centigrade and
Fahrenheit Temperature
Scales
°C
–30 –25 –20 –17.8 –15 –10 –5
0
5
10
15
20
25
30
35
–22 –13 –4
32
41
50
59
68
77
86
95 104 122 140 158 176 194 212
–0
5
14
23
40
50
60
70
80
90 100
°F
Fig. 2-6
752f206
TOYOTA Air Conditioning and Climate Control – Course 752
2-5
Section 2
Basic A/C
System
A basic A/C system has a high-pressure side and a low-pressure side.
The high-pressure side (shown in red below) includes the compressor,
condenser and the receiver/drier. The low-pressure side of the system
(shown in blue below) includes the expansion valve and the evaporator.
Refrigeration Cycle
Vehicle
A/C System
Evaporator Cold
Low-Pressure,
Low-Temperature
Gas
Air
Expansion
Valve
HeatSensing
Tube
Suction
Service
Valve
Blower Motor
Liquid
Refrigerant
Car Interior Air
Hot Air
Discharge
Service
Engine Cooling Fan
Valve
HighTemperature,
High-Pressure
Gas
Receiver
Compressor
Condenser (Liquefies)
High-Pressure,
High-Temperature
Liquid
Fig. 2-7
752f207
Here is the basic flow through the system. Beginning with the low side,
the expansion valve controls the flow and pressure of liquid refrigerant
into the evaporator (heat exchanger). As the lower pressure liquid
refrigerant turns into a gas inside the evaporator, a tremendous amount
of heat is absorbed from the warm passenger compartment air circulating
over and around the evaporator. The A/C blower motor helps circulate air
throughout the vehicle’s interior. The still gaseous, but very hot refrigerant
then flows into the compressor.
The compressor pressurizes the gaseous refrigerant. The high-pressure
refrigerant then flows to the condenser (heat exchanger) where the absorbed
heat in the refrigerant transfers to the air outside the vehicle. A “condenser”
fan helps this heat transfer process. As heat is removed from the refrigerant,
it changes from a gas back to a liquid. The liquid refrigerant is then ready
for another cycle through the system. The receiver-drier acts as a filter
and storage tank for refrigerant before entering the expansion valve.
2-6
TOYOTA Technical Training
The A/C System
System Pressure
All automotive A/C systems are now based on HFC-134a refrigerant.
Because of this, all systems have similar characteristics.
Even though current vehicles use less refrigerant or a smaller volume
of refrigerant, system pressure will be about the same under similar
conditions. Therefore, the pressures within a working system will provide
the technician with an accurate measure of the following:
• Amount of refrigerant in the system
• Operation of the compressor
• Degree of pressure regulation provided by the expansion valve
• Efficiency of the condenser to dissipate heat (dirt or bugs reduce
efficiency)
For these reasons, the system pressures (high and low) will provide
useful diagnostic information.
TOYOTA Air Conditioning and Climate Control – Course 752
2-7
Section 2
The A/C system uses the properties of refrigerant to remove heat from the
passenger interior.
The A/C system contains two pressure zones: low and high pressure.
The low pressure portion of the system contains the expansion valve and
the evaporator.
The high pressure portion of the system contains a compressor,
condenser and a receiver-drier.
There are two heat exchangers in the system: A condenser (gets rid of
heat) and an evaporator (absorbs heat).
Electric fans assist heat transfer: An A/C blower fan for the evaporator
and a fan for the condenser.
The entire system is connected by high and low pressure hoses (hard and
flexible lines).
2-8
TOYOTA Technical Training
Section 3
A/C System Components
Lesson
Objectives
1. Identify A/C System Components, and their function in the
refrigeration circuit.
2. Identify and verify the changes in pressures within the A/C refrigeration
circuit during operation.
3. Identify circuit protection devices and their role in the A/C system.
4. Locate and identify front and rear A/C System Components on a
vehicle and vehicle simulator.
TOYOTA Air Conditioning and Climate Control – Course 752
Section 3
A/C System Components
In the previous sections, we referred to the functions of the A/C
components. Here’s how each one works in closer detail.
A/C System
Components
Evaporator
Expansion
Valve
Receiver-Drier*
Condenser
Expansion
Valve
Compressor
Fig. 3-1
752f301
The expansion valve receives liquid refrigerant from the high-pressure
components (compressor and receiver/drier). In order for the system to
develop pressure, the flow of refrigerant must be met with a restriction.
The expansion valve provides the needed restriction in the system. It
creates the difference between the high-pressure side of the system and
the low-pressure side.
Capillary Tube
Traditional
Expansion Valve
Controls amount of
refrigerant into
evaporator core.
*Built into
sub-cool condenser
on some models
Diaphragm
Chamber
Diaphragm
Equalizer Circuit
(for Internal
Equalizer Type)
Valve
Outlet
HeatSensing
Tube
Inlet
Pressure
Spring
Fig. 3-2
752f302
TOYOTA Air Conditioning and Climate Control – Course 752
3-1
Section 3
Most Toyota models now use a block-type expansion valve where both the
evaporator inlet and outlet pass through the valve assembly. The capillary
tube is located inside the stream of refrigerant leaving the evaporator.
Due to the low temperature at this point, the valve is subject to blockage
by microscopic debris or internal ice if any water is present in the
refrigerant. Because of this, every system has some method to filter
out these elements.
Block-Type
Expansion Valve
Releases high
pressure refrigerant into
evaporator.
Valve
Fig. 3-3
752f303
Not all vehicles use an expansion valve like the one described above. Some
have a pressure-regulator at the outlet end of the evaporator. Other
manufacturers use a fixed-opening orifice tube to create the pressure
drop at the entry to the evaporator. This type of expansion valve relies on
the cycling of the compressor clutch to vary the flow and prevent icing.
The expansion valve is located at the inlet of the evaporator. A small
passage creates a pressure drop as the refrigerant enters the evaporator.
The pressure drop occurs as the small spray of refrigerant expands to fill
the large volume inside the tubes of the evaporator. Here is the sequence
of events:
• Warm, high-pressure liquid refrigerant flows to the expansion valve
• A low-pressure spray of cold refrigerant droplets pass through the
expansion valve into the evaporator
• As the cold spray contacts the relatively warm tubing of the evaporator,
the refrigerant vaporizes (becomes a gas) and absorbs heat from
the evaporator and the air surrounding the evaporator
3-2
TOYOTA Technical Training
A/C System Components
Evaporator
The action between the expansion valve and the evaporator is the key to
heat transfer in the system. The evaporator is the heat exchanger for the
low-pressure side of the system. It is the key heat exchanger in the A/C
system. All incoming or recirculated air passes through the evaporator. In
doing so, the evaporator absorbs heat from the cabin air (car interior) or
incoming fresh air so this heat can be carried to the condenser.
Evaporator
• Removes heat from
interior as refrigerant is
released into the core.
• Dehumidifies air by
condensing moisture on
the fins.
Fig. 3-4
752f304
Evaporators are typically multiple-flow designs and made from aluminum.
Since the surface fins or plates of the evaporator are usually colder than
the air flowing past them, any moisture (water vapor) in the air tends to
condense and form liquid droplets on the fins. The moisture eventually
drains from the evaporator case through a drain hose to the ground. This
process is called dehumidification.
This process of dehumidifying is not only important to passenger
comfort, but can also be used in cold or humid climates to reduce
windshield fogging. However, a large amount of heat must be removed
from water vapor in order to condense it, so extreme humidity reduces the
ability of the evaporator to lower the temperature of the incoming air.
TOYOTA Air Conditioning and Climate Control – Course 752
3-3
Section 3
Expansion
Valve/
Evaporator
Interaction
Since the evaporator surface temperature can be close to 32° F (0° C),
there could be a problem in high humidity conditions when moisture
vapor condenses on the evaporator and freezes. This frozen water forms
an insulating layer that prevents air from reaching the evaporator to
exchange heat.
In order to prevent icing, the expansion valve can change the size of
the spray orifice (opening). The size of the orifice is controlled by a
spring-loaded diaphragm that moves according to a heat-sensing tube
(bulb). This bulb, called the capillary tube is located at the outlet of the
evaporator. A thin, hollow tube connects the sensing tube to the
diaphragm chamber. The sensing tube contains refrigerant and senses the
evaporator temperature which changes the pressure inside the tube. The
capillary tube transfers this pressure to the diaphragm to push against
the spring and open the expansion valve to control refrigerant flow to the
evaporator. Less flow = less heat transfer; more flow = more heat transfer.
For example, if there is a high heat load in the vehicle, the evaporator
temperature will be relatively high (more heat transfer). The refrigerant
in the sensing tube will therefore expand and the increased pressure will
tend to open the expansion valve more. This increases refrigerant flow
and heat transfer in the evaporator. When the system stabilizes, the
evaporator surface temperature should remain constant at about
32° F (0° C) in order to provide the greatest heat-removing capacity.
The traditional expansion valve has external equalization. The block-type
expansion valve is internally vented. This helps prevent flooding the
evaporator during operation with a high heat load.
Compressor
The compressor is driven by a drive belt and is a type of pump which
moves a compressible gas, as opposed to a pump that moves a liquid
(e.g. water pump). The air compressor in your repair shop and the intake
and compression strokes in a 4-stroke cycle engine are two other examples
of compressors.
In order for the refrigerant to exchange heat at the condenser, it must be
hotter than the air outside the vehicle. The compressor accomplishes this
by raising the pressure, and therefore, the temperature of the refrigerant.
3-4
TOYOTA Technical Training
A/C System Components
An important difference between a compressor and a pump is that a
compressor cannot pump liquids. Since liquids cannot be compressed,
a compressor filled with liquid will either lock up or break depending on
the amount of torque applied to its pulley by the engine crankshaft. More
commonly, the reed valve assembly that controls gas flow inside will be
destroyed when a compressor hydraulically locks.
Most compressors have a “bolt-on” fitting block to provide connections to
the low-pressure side of the system (suction side) and high-pressure side
of the system (discharge port). There may also be fittings on or near the
compressor to connect pressure gauges.
Reed Valve Control
of Refrigerant Flow
Discharge Reed Valve
Reed valves control
both suction and
discharge flow.
Discharge Reed Valve
Fig. 3-5
Suction Reed Valve
752f305
Various Toyota vehicles use or have used one of the following types of A/C
compressors:
•
Piston
•
Through-Vane
•
Swash-plate
•
Variable Capacity
•
Scroll-type
Piston-type compressors have valves to control the flow of intake and
exhaust gases. For simplicity, A/C compressors use spring-tensioned
stainless steel reed valves which allow gas flow in one direction and only
when a significant pressure difference exists between the chamber of the
compressor and the intake or outlet passages. The earliest compressors
were belt-driven using two- or three-pistons with connecting rods and a
TOYOTA Air Conditioning and Climate Control – Course 752
3-5
Section 3
crankshaft supported by ball bearings. Lubrication is provided by a
splash from a sump in the compressor base. Construction of reciprocating
compressors are very similar to a four-stroke cycle lawn mower engine.
Suction
Piston-type A/C
Compressor
Discharge
Reed Valve Construction.
Down-Stroke
Up-Stroke
Fig. 3-6
752f306
Through-Vane (TV) compressors replaced reciprocating, piston-type
compressors. Through-vane compressors reduce rotating mass by
eliminating pistons in favor of sliding vanes which seal against the
compressor housing at both ends. These compressors are lubricated by
oil from a pressurized chamber in the rear of the compressor.
Discharge Reed Valve
Through-Vane
Compressor
Discharge Valve
Exhaust Port
Rotor
Sludging Valve
Vane
Through-Vane
Rotor Housing
Intake Port
Fig. 3-7
752f307
With four pulses per revolution, TV compressors provide high efficiency
and minimal vibration. However, unlike conventional compressors that
build pressure against a reed valve until it opens, TV compressors
perform compression internally. Because of this, they tend to run hotter
than conventional compressor designs. In addition, for this reason, they
are equipped with an internal pressure release called a sludging valve.
3-6
TOYOTA Technical Training
A/C System Components
This valve prevents damaging the through-vanes or the reed valve (which
should “see” only refrigerant gas) by allowing liquid oil to escape from the
compression area into an oil chamber.
Some Toyota vehicles use a swash-plate (also called “wobble plate”) type
compressor. Some models use multiple, opposed pistons arranged around
a single swash-plate with two compression chambers for each cylinder.
The cylinders connect to reed valves and common inlet and outlet passages
at each end. The swash-plate converts the rotary motion of the shaft into
smooth back and forth motions of the pistons. This design provides
reduced vibration and allows more pulses per revolution than a two-piston
reciprocating compressor.
TOYOTA Air Conditioning and Climate Control – Course 752
3-7
Section 3
The Variable Capacity swash-plate compressor uses a solenoid control
valve that opens and closes to adjust the low-pressure inlet to the
compressor. Controlling the suction side of the compressor changes the
volume capacity according to the cooling load of the A/C system. This
change in pressure affects the swash-plate angle. It also changes the piston
stroke and thus the amount of refrigerant discharged to the condenser.
Controlling the compressor volume in this manner improves A/C
performance and energy savings.
Variable Capacity
Compressor and
Solenoid Valve
Crank Chamber
Shoe
Piston
Variable stroke of pistons.
Shaft
Solenoid
Control Valve
Piston
Lug Plate
Cylinder
Swash-Plate
Heat Load: Large
Fig. 3-8
752f308
Heat Load: Small
Solenoid Control Valve
Solenoid Control Valve
Low Pressure: High
Low Pressure: Low
Internal Pressure
of Swash-Plate
Chamber: Low
Internal Pressure
of Swash-Plate
Chamber: High
Swash-Plate Angle: Large
Swash-Plate Angle: Small
Piston Stroke: Large
Piston Stroke: Small
Cooling Performance: Large
Cooling Performance: Small
Fig. 3-9
752f309
3-8
TOYOTA Technical Training
A/C System Components
A Scroll Compressor is a spirally wound, fixed scroll and variable scroll
that form a pair. The fixed scroll is integrated with the housing. The
rotation of the shaft causes the variable scroll to rotate while maintaining
in the same space. Thus, the volume of the space that is created by both
scrolls varies. This changing volume creates the suction, compression and
discharge forces needed for refrigerant gas flow through the compressor.
Note:
Some hybrid models use an electrical motor drive scroll-type compressor
to continue operation even when engine stops (refer to page 3-10).
Scroll Compressor
Scroll-type A/C
Compressor
Shaft
Magnetic
Clutch
Intake
Port
Oil Separator
Discharge
Port
Pins
Variable
Scroll
Operation
Fixed
Scroll
Fixed Scroll
Discharge
Port
Fig. 3-10
Fig. 3-11
752f310
752f311
Suction:
As the capacity of the compression chamber which is created between the
variable scroll and the fixed scroll increases with the revolution of the
variable scroll, refrigerant gas is drawn in from the intake port.
Compression:
As the variable scroll revolves, the capacity of the compression chamber
gradually decreases. As a result, the refrigerant gases drawn in become
compressed and are sent to the center of the fixed scroll. The refrigerant is
completely compressed when the variable scroll completes approximately
2 revolutions.
Discharge:
After the refrigerant is compressed (refrigerant gas pressure high), the
refrigerant gas exits through the discharge port in the center of the fixed
scroll via the discharge valve.
TOYOTA Air Conditioning and Climate Control – Course 752
3-9
Section 3
Scroll Compressor
Cycle
Suction
Discharge
Port
Intake
Port
Fixed
Scroll
Variable
Scroll
Compression
Discharge
Fig. 3-12
752f312
Some scroll compressors in Toyota vehicles contain a built-in oil separator.
This chamber helps separate the compressor oil from the refrigerant that
circulates in the refrigeration system. Excess oil in the scroll section of
the compressor can lower compressor efficiency and in some cases,
damage it.
3-10
TOYOTA Technical Training
A/C System Components
Compressor
Clutch
A drive belt from the crankshaft pulley drives the compressor. Some
systems use V-belts and some use a flat, multirib belt to help reduce
frictional loss and noise. On some models, a single serpentine V-belt
drives all the engine accessories including the A/C compressor. In this
kind of system, an automatic tensioner maintains the correct serpentine
belt tension.
Idler Pulley
Serpentine Belt
System
Some models have
a single belt that drives
multiple components.
A/C
Compressor
Pulley
Fig. 3-13
Crankshaft Pulley
752f313
The compressor clutch engages and disengages the compressor as needed.
With the clutch disengaged (not energized), there is no refrigerant flow
and the compressor pulley spins freely.
Compressor Clutch
Engages compressor by
electromagnetic action.
Stator Coil
Rotor
Shim
Bearing
Pressure Plate
Fig. 3-14
752f314
The single-plate clutch has an electromagnetic pressure plate to allow
the compressor pulley to freewheel or drive the compressor as conditions
demand. The clutch is normally disengaged. When a relay is energized,
the electromagnetic coil pulls the spring-loaded pressure plate into
the clutch.
TOYOTA Air Conditioning and Climate Control – Course 752
3-11
Section 3
The electromagnet allows A/C operation to be controlled by an electric
circuit. The compressor clutch relay is also controlled by a temperature
signal from the evaporator and a pressure switch in the refrigerant line.
In most systems, the compressor clutch cycles ON and OFF periodically to
allow the evaporator to warm up (defrost) during periods of high cooling
demand. An evaporator cold enough to freeze moisture around it does not
transfer heat as well.
Some variable capacity compressors don’t use a magnetic clutch. Instead
they use a Damper Limiter (DL)-type drive pulley. This pulley uses a
damper to absorb torque fluctuations of the engine and a limiter
mechanism. In case the compressor locks, the limiter mechanism causes
the spoke portion of the pulley to break. This separates the pulley from
the compressor shaft and prevents the drive belt from breaking. To
reduce pulley weight, the pulley portion is made of plastic.
Damper
Limiter Pulley
• Absorbs torque
fluctuations.
Spoke
Portions
Pulley Portion
(Plastic)
Rotate Direction
• Protects drive belt if
compressor locks.
Damper
Damper
Limiter Mechanism
Fig. 3-15
752f315
3-12
TOYOTA Technical Training
A/C System Components
Condenser
In order to condense hot refrigerant gas (vapor) from the compressor
discharge port into a liquid, heat must transfer out of the refrigerant into
the outside air. To do this, the condenser is located in front of the radiator
in the air stream so the maximum temperature differential exists to
transfer the heat. Condensers are typically made of aluminum and have a
single flow or serpentine path (as shown) which increase the time available
for heat transfer. Some systems now use multiple-path condensers with
two or three shorter serpentine sections connected in parallel. This
maximizes the time the refrigerant stays in the condenser for increased
heat transfer.
Condenser
• Condenses hot,
high pressure gases
into a liquid.
• Heat dissipates to
outside air.
Tube
Gaseous
Refrigerant
Liquid
Refrigerant
Fin
Fig. 3-16
752f316
TOYOTA Air Conditioning and Climate Control – Course 752
3-13
Section 3
Many Toyota vehicles now use a sub-cool condenser that helps separate
the liquid from the gaseous refrigerant. In this design, the condenser
redirects gaseous refrigerant to the top for further cooling (gas-to-liquid)
while the liquid refrigerant exits from the bottom. This ensures all
refrigerant sent to the evaporator is in a liquid state.
Sub-Cool
Condenser
• Current models use
sub-cool type.
Multiflow Condenser
Condensing Portion
Modulator
Gaseous
Refrigerant
• Super cooling portion
more efficiently
changes gaseous
bubbles into liquid.
Liquid
Refrigerant
Fig. 3-17
Super-Cooling Portion
ReceiverDrier
752f317
The amount of refrigerant flowing through the system varies depending on
heat load and ambient (outside) temperature. Because of this,
extra refrigerant must be available for these different conditions. The
receiver-drier acts as a storage tank for extra refrigerant. It also contains
a filter and a desiccant material in an internal sack to help remove
moisture in the system.
Receiver-Drier
Sight Glass
• Removes moisture
from refrigerant.
IN
• Stores liquid refrigerant.
• Filters refrigerant.
OUT
Receiver
Tube
Drier
Desiccant
Receiver
Body
Filter
Fig. 3-18
752f318
3-14
TOYOTA Technical Training
A/C System Components
The outlet of the receiver-drier connects to a siphon tube that goes to the
bottom of the container. This acts as a liquid/vapor separator and ensures
only liquid refrigerant is supplied to the expansion valve. In addition,
the end of the siphon tube has a very fine mesh screen to filter debris from
the refrigerant and oil. This protects the expansion valve and the
compressor from mechanical damage.
To protect the expansion valve from being blocked by ice, any moisture
in the refrigerant is removed as it passes through a desiccant in the
receiver-drier. A desiccant is a chemical that bonds water (H2O) with other
molecules to form a different molecule. There is a limit to the amount of
moisture the desiccant can hold. After the desiccant becomes saturated,
any additional moisture will pass through the system. A receiver-drier left
open (fittings removed) on the shelf or in the vehicle for about 10 minutes
(80% humidity) will become fully saturated and unusable.
The receiver-drier desiccant material is different in HFC134a and older
CFC-12 systems. Do not interchange them. Moisture inside the system
is absorbed by the desiccant and is not fully removed during system
evacuation or the vacuum process prior to recharging. Moisture remaining
inside the system or receiver-drier can result in internal icing of the
expansion valve and cause erratic system operation.
Note:
The receiver-drier is a service part and should be replaced any time
the system has leaked, or been left open (even for a short time), or when a
component such as a compressor or reed valve has failed.
In some systems, the receiver-drier contains a sight glass that allows you
to visually confirm that only liquid refrigerant is passing on to the
expansion valve. This may be useful during preliminary diagnosis, but it
is not accurate in determining if the system has the proper amount of
refrigerant. Some models use a “modulator-drier” that is part of the
condenser. On some Toyota models, the functions of a receiver-drier are
built into the sub-cool condenser; desiccant is stored in the modulator
portion of the sub-cool. On other models, the receiver-drier is separate
from the sub-cool condenser.
TOYOTA Air Conditioning and Climate Control – Course 752
3-15
Section 3
Pressure
Relief
Devices
For safety, every pressurized system must have some sort of pressure-relief
system to reduce excess system pressure before it can become a hazard.
In an A/C system, a fusible plug was one type of safety device. A fusible
plug is a hollow bolt filled with a soft, low-temperature solder. The plug
then threads into the top of the receiver-drier. If the pressure in the high
side of the system exceeds a predetermined limit (400 psig or 30 bar) or if
the temperature exceeds 220° F (110° C), the solder melts out of the bolt
and the pressurized gas escapes. On current models, a pressure switch
de-energizes the compressor when system pressure becomes excessive.
Possible causes of excessive pressure or temperature:
• Restriction in the high side of the system
• Overheating condenser due to restricted airflow or fan failure
• System overcharged with refrigerant
• Abnormal heat source (e.g. steam cleaner)
After the system is repaired replace the receiver-drier.
On some other vehicles, a pressure relief valve performed the function
of the fuse plug. Threaded into the compressor valve assembly, the relief
valve opened when the system pressure exceeded 400 psig (30 bar). It
only stayed open until the pressure fell below a lower limit. That avoided
a total loss of refrigerant. A/C systems using a relief valve may also have
a pressure switch to de-energize the compressor as described above.
Although effective, this type of safety device vents refrigerant to the
atmosphere, which is no longer allowable.
Note:
3-16
The pressure relief valve was not designed to reseal after it opened. If you
suspect the valve has opened, replace it after recovering the remaining
refrigerant in the system and repairing the cause of the malfunction.
TOYOTA Technical Training
A/C System Components
Multipressure
Switch
There may be one or more pressure switches in the refrigerant lines.
Current models use a Multipressure Switch that contains two or even
three pressure-sensing circuits. It is located in the high-pressure line of
the system (between the compressor and expansion valve).
• Low pressure – The low-pressure sensing circuit switches the compressor
OFF. This prevents system damage due to the reduced amount of
lubricant as a result of low system pressure. An external leak will also
be detected by this sensing circuit.
• Medium pressure – The A/C control unit monitors pressures within
this range to control the operation of the high-speed condenser fan.
• High pressure – Excessively high system pressure indicates a malfunction.
This sensing circuit switches OFF the compressor clutch to prevent
system damage.
Note:
The term “psig” indicates gauge pressure that takes into consideration
atmospheric pressure of 14.5 pounds per square inch and displays it as “0”
on a pressure gauge.
Multipressure
Switch
Magnetic Clutch Control
Source Voltage
Medium
Pressure
(NC)
4 Pins
3 Pressures
Fig. 3-19
752f319
Condenser Fan
(High Speed)
Source Voltage
Low
Pressure
(NC)
High
Pressure
(NC)
Compressor
Clutch
Fig. 3-20
752f320
During normal operation, the amplifier cycles the compressor clutch
ON and OFF to maintain an evaporator temperature of approximately
32° F (0° C). When the amplifier detects a malfunction in the system, it
will de-energize the compressor clutch and flash the A/C signal lamp.
A Diagnostic Trouble Code will generate and will stay in memory until
the ignition switches OFF.
Lines and
Hoses
Refrigerant flows through the system in rigid metal lines and flexible
rubber hoses. Connections at each component and between lines provide
convenient installation in the vehicle as well as to service and repair
system components. The volume of refrigerant is always the same at
any point in the system (since it is a closed system). However, since the
high-pressure side has a high-density liquid, it uses much smaller
diameter lines than the low side. As a rule:
TOYOTA Air Conditioning and Climate Control – Course 752
3-17
Section 3
• The high-pressure lines are smallest in diameter.
• The low-pressure lines have the largest diameter.
Hose Fittings On
Receiver-Drier
Block-type fittings
help position and
secure piping.
Fig. 3-21
752f321
Unlike stationary refrigeration systems (appliance or building), mobile
A/C systems must operate under high levels of vibration and motion. For
this reason, all joint fittings use a gasket or O-ring to help seal the system.
O-rings are made of various materials; each selected to deal with the
particular refrigerant and lubricating oil used.
Fittings are typically one of three types: threaded tube-type, block-type or
quick-disconnect. Threaded fittings are used between hoses and lines. The
more rigid block fittings are used at system component. Block fittings
provide more accurate positioning of the sealing surfaces, and they reduce
the risk of tearing an O-ring due to rotation during assembly.
Older vehicles equipped with CFC-12 refrigerant have threaded metric
fittings. Other vehicles may use metric or SAE (inch unit) threads for
CFC-12. Fittings in a HFC-134a system are always metric and do not have
notched corners on the hex nuts for identification.
Thread-Type
Fittings
• HFC-134a “O” ring
slip-type fit.
• CFC-12 “O” ring was
crush-type fit.
• CFC-12 fittings have
notch in nut position.
HFC-134a
3-18
TOYOTA Technical Training
CFC-12
Fig. 3-22
752f322
A/C System Components
A quick-disconnect type fitting uses a plastic clamp lock to connect the
tube endings. This type of fitting has no threads. One tube end has
an O-ring that fits into a mating tube end. The plastic clamp keeps the
tube ends together to create a leak-free seal. To service the system
(e.g. evacuating the system — the system must be empty), a special
remover tool is used to release the clamp.
Quick-Disconnect
Fitting
Clamp
• Clamp holds tubes
in place.
• See removal SST
page 4-11.
A/C Tube
A/C Tube
Note: When assembled,
clamp can still rotate.
Fig. 3-23
752f323
With threaded or threadless tube fittings, in order to ensure the proper
seal under high system pressures and temperatures, A/C O-rings rest
within a machined area instead of just being compressed between two
surfaces like a common gasket. In order to ensure a correct seal, the
O-ring must be the correct one. An O-ring that looks about right may
make a joint impossible to assemble without damage or may result in a
leak. O-rings should be lubricated with the correct system refrigerant oil
to prevent nicks or scratches during assembly.
Note:
With threaded fittings, the correct tightening torque is important for a
proper seal. Too little torque will not provide enough pressure on the
O-ring to seal and may allow the fitting to move. Too much torque may
distort the fitting and make it difficult to disassemble later. Torque
specifications for the different types and sizes of fittings are described in
the Vehicle Repair Manual.
In order to apply the right tightening torque, the threads must be
lubricated with oil. To prevent twisting and to relieve tension on rigid and
flexible lines, hold one fitting stationary with an open-end or flare-nut
wrench while tightening the other fitting. In the case of a threaded tube
fitting, the male end should be held while tightening the female threaded
nut.
TOYOTA Air Conditioning and Climate Control – Course 752
3-19
Section 3
Cooling
Fans
The effectiveness of the A/C system depends on removing heat as the hot
refrigerant flows through the condenser. Because of this, cooling fans
become more critical when the A/C system is ON. There are two fans that
contribute toward heat transfer in the engine compartment:
• A/C Condenser Fan
• Engine Cooling Fan
A/C Condenser Fans are driven either manually from the engine or
electrically. Some Toyota vehicles use a belt-driven fan. Most current
vehicles use electric fans. A fan circuit contains the following components:
• Coolant Temperature Switch (thermo-switch) located in the water jacket
of the cylinder head. The coolant temperature switch is normally closed
(NC). When the coolant temperature is cold/cool, the circuit path
through the switch is complete (ON). The switch opens (OFF) when
the coolant temperature exceeds a specified value, typically around
190° F (90° C).
Cooling Fans
Two types:
Mechanically or
Electrically driven.
Pulley
Fluid
Coupling
Fan Bracket
Cooling Fan
Engine Cooling Fan
Condenser Fans
Fig. 3-24
752f324
3-20
TOYOTA Technical Training
A/C System Components
Electric Cooling
Fan Circuit
1 2F
Fan relays activate
cooling fans at low or
high speed depending
on coolant temperature
or system pressure.
1
5
Engine
Main
Relay
3
2
30A
CDS
FAN
30A
RDI
FAN
4
10 2A
1
W
1
2D
3
2
Radiator
Fan Relay
L
M
4
1
R
2
A1
A/C Condenser
Fan Motor
8 2A
2 2D
4 2A
6 2D
5
B
L
B-R
L-B
4
Radiator
Fan Relay
No. 2
3
5
1
2
2
5
5
B-R
2
B-w
B-R
R1
Radiator
Fan Motor
M
1
B-R
1 EA1
W-R
A2
A/C High
Pressure SW
1
W-B
5
5
5
1
2
5
3
Radiator
Fan Relay
No. 3
W3
Water Temp.
SW
1
1
2
5
5
W-B
W-B
W-B
3 2A
From Magnetic
Clutch Relay
<26-4><27-5>
3 2E
B
W-B
EB
W-B
W-B
2 EA1
Front Left Fender
Front Left Fender
EB
Fig. 3-25
752f325
Electric cooling fan systems were first used in transverse-mounted
engines in front-wheel drive vehicles (the drive belt is not near the
radiator). Since the fan(s) is electrically powered, various sensors can
control fan operation.
TOYOTA Air Conditioning and Climate Control – Course 752
3-21
Section 3
• Refrigerant Pressure Switch. This switch normally monitors refrigerant
pressure in the high-pressure side of the system (between the
compressor and the expansion valve). If the pressure is too high or
too low, the pressure switch opens to stop the compressor (via the
compressor clutch). A mid-pressure setting on many cars also controls
the high speed operation of the electric condenser fans.
• Normally Open Relays control the condenser fan(s) when the
thermo-switch and pressure switches are closed. However, when either
switch opens (sensing excessive pressure or temperature), the relays
are connected in the circuit to energize the fans. The wiring diagram
on the previous page shows a typical system that uses two fans that
may rotate at different speeds. With this circuit, three relays are used
to connect each fan to power or ground. This means that the two fans
can each be connected to power and ground for high speed operation
(parallel circuits) or they can be connected in series so each fan sees
about half of battery voltage (about 6 volts) for low speed operation.
• In the circuit, if either sensor shows high resistance (caused by a loose
wire or corroded terminal) the fans will always run at high speed.
A fail-safe circuit in the cooling fan ECU protects the system in case of a
component failure.
A/C
Blower
Motor
A multispeed fan motor in the air conditioning ductwork circulates cabin
(interior) air or fresh exterior air through the evaporator. In early Toyota
vehicles, a multi-position switch and resistor assembly in the circuit
changes the source voltage to the fan motor. The resistor block contains
multiple outlet terminals to introduce different resistance values into the
circuit to create the multiple speeds. At its highest speed, a full 12 volts
is supplied to the blower motor. To reduce blower speed, the switch
introduces a different resistance to create each of the lower blower speeds.
In current Toyota vehicles, the blower speed is controlled electronically
by the A/C controller.
Resistor-Type
Blower Switch
Current passes through
some or all portions
of resistor depending on
blower switch speed
position.
12V
Lo
M
Fan Motor
Blower Switch
Hi
Resistor Block
Fig. 3-26
752f326
3-22
TOYOTA Technical Training
A/C System Components
Review of
Refrigeration
Circuit
Based on the physics of heat transfer, an automotive A/C system works
on these principles:
• Heat is absorbed from the passenger compartment by the evaporator.
This happens because the expansion valve restricts the flow of liquid
refrigerant and increases pressure. However, when the expansion valve
opens, there is a drop in pressure which causes the refrigerant to
evaporate and absorb heat. Dehumidification occurs as the interior air
is drawn across the cool surface of the evaporator.
• The gas coming out of the evaporator has its pressure and temperature
raised by the compressor.
• The hot gas releases heat to the outside air at the condenser and
changes (condenses) back into a liquid before being filtered and stored
at the receiver-drier.
A/C Refrigerant
Cycle
Fig. 3-27
752f327
TOYOTA Air Conditioning and Climate Control – Course 752
3-23
Section 3
Notes
3-24
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 3-1 (IN-CLASS)
A/C Principles
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
Describe and identify basic terms, properties and information about vehicle refrigerants.
Background:
Servicing mobile refrigerant systems require a knowledge of service procedures as well as the properties of
different refrigerants.
Tools and Equipment:
• This worksheet
1. Compliance in handling refrigerants is covered by what law?
________________________________________________________
2. The release of refrigerant into the atmosphere can damage the ____________________ layer that protects the
earth from excessive __________________________________________ and skin cancer.
3. CFC-12 is a _________________________________________ and HFC-134a is a
______________________________________.
4. It is unlawful to release ____________________ or ____________________ refrigerant into the atmosphere.
5. Refrigerant must be ___________________________ from the A/C system before ________________________
the A/C system.
6. What test should be done before recovering refrigerant from a vehicle? _______________________________
7. Recovered refrigerant can be reused if it is _________________________ and service equipment that recycle
the refrigerant during recovery are known as _________________________ machines.
8. Placing a vacuum on the A/C system with a vacuum pump for __________________________ to remove
__________________________ is known as _____________________________.
TOYOTA Technical Training
3W1-1
Worksheet 3-1
9. What does it mean if, following recovery and evacuation, the pressure gauge raises when the vacuum is
removed?
___________________ or _______________________________________________________________________,
which should be _______________________________.
10. When should the evacuation be done?
_______________________________________________________________________________
11. A/C service fittings for HFC-134a have _______________________________________ for low and high sides
and also have _________________________________ within ___________________________________.
12. There is a difference between CFC-12 and HFC-134a service fittings. The CFC-12 service fittings are
_____________________________________ type, while the HFC-134a service fittings are the
_____________________________________ type.
13. A/C service hoses are color-coded. Low-pressure side hoses are _____________________ in color, while
high-pressure hoses are _____________________ in color.
14. CFC-12 containers are _____________________ in color, while HFC-134a containers are
_____________________ in color.
15. Halogen leak-detectors can detect refrigerant leaks of __________________________________ leakage or
more per year.
16. HFC-134a refrigerant is ________________________ than air, which means the leak-detector sensing probe
should be held ________________________ suspected leak points.
17. Detecting leaks on the low side is often more effective with the A/C turned __________________. High-side
leaks are more easily detectable with the system __________________to increase pressures.
18. The location to check for evaporator leaks is at the evaporator case ______________________________.
19. Suspected leak areas such as the compressor seal will often have ______________________________.
20. Refrigerant dyes are generally ___________________ recommended?
3W1-2
TOYOTA Technical Training
A/C PRINCIPLES
21. Refrigerant dyes can ___________________________________________ or if added with PAG oil can cause
______________________________ when looking for leaks.
22. Debris in the A/C system following a compressor failure is _____________________________________ from
components and lines.
23. If debris is trapped in a condenser or evaporator it should be ___________________________.
24. Flushing is not recommended due to ____________________________________________________.
25. “PAG” oil is used with _________________________ type refrigerant.
26. “Mineral” compressor oils are used with ________________________ refrigerants.
27. What is the application for Denso oils numbered ND-6 _________________________,
ND-7_________________________, ND-8 _________________________, ND-9 _________________________
28. The A/C works very well to __________________________ windows in rainy weather.
29. When using the A/C in cold weather, remember the ________________________________ may be
__________________________.
30. Unusual A/C clutch noises during engagement could be related to _________________.
31. The A/C compressor clutch gap is adjusted using _______________________.
32. When installing a REMAN compressor, it is important to check for _______________________ in the system.
33. Whenever the A/C system has been opened to the atmosphere, or a component is replaced, you should also
replace the __________________________________, then ___________________________ the system.
34. A/C odors are caused by _______________________ on the __________________________________.
Instructor Sign Off: ______________________________________
TOYOTA Technical Training
3W1-3
Worksheet 3-1
Notes
3W1-4
TOYOTA Technical Training
A/C PRINCIPLES
A/C Principles
Name: ___________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 3-1 using the A/C Principles worksheet in the classroom. Ask the instructor if you have
any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
A/C technician certification requirements
Refrigerant recovery requirements
A/C recovery and charge station
requirements
Refrigerant containers and cross
contamination issues
Noncondensable gas (air) purging
TOYOTA Technical Training
3W1-5
Worksheet 3-1
Notes
3W1-6
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 3-2 (ON-CAR)
A/C Component Identification
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
Locate and identify system components in both front and rear A/C units.
Background:
Successful diagnosis and troubleshooting requires identifying and knowing where the various A/C components
are located.
Tools and Equipment:
•
Vehicle Repair Manual
•
TIS Machine
•
Toyota vehicle with Auto A/C and rear A/C if available
Section 1
Identify Basic A/C Components
1. Using the Vehicle Repair Manual and NCF Manual, locate and identify the following basic A/C components:
Component
Vehicle
General Location
Compressor
Multipressure switch
Expansion valve
High-pressure A/C service fitting
Sight Glass
Low-pressure A/C service fitting
Heater water valve and water
valve control cable servo-motor
Sub-cool condenser and modulator
Sub-cool condenser dryer access
Evaporator assembly
Heater unit
Blower assembly
Instructor Sign Off: ______________________________________
Stop: Do not proceed without Instructor’s approval
TOYOTA Technical Training
3W2-1
Worksheet 3-2
Section 2
Identify Auto A/C Components
2. Using the Vehicle Repair Manual and NCF Manual, locate and identify the following auto A/C components:
Component
Vehicle
General Location
Ambient temperature sensor
Air mix servo-motors
Room (interior) temperature sensor
A/C ECU
Solar sensor
Clean air filter
Instructor Sign Off: ______________________________________
3W2-2
TOYOTA Technical Training
A/C COMPONENT IDENTIFICATION
A/C Component Identification
Name: ___________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 3-2 using the A/C Component Identification worksheet in the shop. Ask the instructor if
you have any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
Location and type of compressor
Location and type of condenser
Location of filter-drier (receiver-drier)
Location and purpose of sight glass
Low-side and high-side A/C Fittings
Hot water (heater) valve
Fresh air filter (cabin filter)
A/C controls and sensor locations
A/C evaporator and servo-motors
TOYOTA Technical Training
3W2-3
Worksheet 3-2
Notes
3W2-4
TOYOTA Technical Training
Section 4
Diagnosis and Repair
Lesson
Objectives
1. Demonstrate systematic diagnosis and the six-step process.
2. Demonstrate leak detection techniques and proper use of a leak detector.
3. Demonstrate refrigerant identification, recovery, recycling, evacuation
and recharging.
4. Successfully operate a refrigerant recovery/recharging machine.
5. Successfully remove and replace the clutch on an A/C compressor.
6. Operate a tester to identify refrigerant contaminants.
7. Locate the leak detector TSB using the TIS, then perform a refrigerant
leak test.
8. Evaluate proper A/C operation using the “Touch and Feel” procedure.
9. Evaluate proper A/C operation by interpreting manifold gauge
pressures.
TOYOTA Air Conditioning and Climate Control – Course 752
Section 4
Diagnosis and Repair
Systematic
Diagnosis
As with any mechanical system, you should conduct a Systematic
Diagnosis of the complaint to repair a nonfunctioning A/C system.
Systematic Diagnosis is:
• Based on a clear understanding of how the system works or should
work.
• A logical, systematic approach to the process of finding the malfunction.
Toyota
Six-Step
Diagnosis
Process
1. Verify the complaint
2. Determine the related symptoms
3. Analyze the symptoms
4. Isolate the cause
5. Correct the cause
6. Check for proper operation
System Checks
A complete check of the mechanics and performance of the A/C system
will quickly reveal areas in need of attention. You can perform simple
and easy-to-do “sight, sound and touch” checks of the A/C system.
These include:
1. Verify outlet temperature (35°– 45° F) with a Performance Test
(see Performance Testing in this section).
2. Coolant Level – An overheated engine will not achieve full cooling
performance.
3. Compressor drive belt tension – At full load, the compressor requires
high drive torque to drive the belt. The Vehicle Repair Manual specifies
the correct tension.
Note:
A blinking A/C light indicates a compressor speed problem from a
slipping, oily or damaged drive belt; slipping, damaged or incorrectly
shimmed compressor clutch; overcharged system causing a slipping belt
or compressor clutch; damaged, loose or intermittently shorted A/C
compressor wire. The least likely causes include an actual compressor
lock-up condition or a malfunctioning lock-up sensor on the compressor.
4. Listen for the loud “click” that indicates the compressor clutch has
engaged (energized). Observe any unusual compressor noises. Confirm
that the electric fans immediately run at low speed.
TOYOTA Air Conditioning and Climate Control – Course 752
4-1
Section 4
5. Look into the sight glass (on receiver-drier, if available):
• It should appear clear, as liquid refrigerant with a few bubbles of
vapor flowing out of the receiver-drier (an almost empty system will
also appear clear).
Sight Glass
Sight Glass
Note: Sight glass not
accurate method to
properly charge system.
Properly
Charged
Insufficiently
Charged
Receiver-Drier
Fig. 4-1
752f401
• Excessive bubbles may indicate an undercharged system.
• A cloudy flow indicates the desiccant has escaped from its bag
container or there is moisture in the system.
• If there is no movement visible, just cloudy streaks, the system is
empty.
6. Carefully touch accessible refrigerant lines to confirm system operation:
• Low-pressure lines should feel cold to the touch. In humid weather,
moisture may condense on these lines.
• High-pressure lines should be hot to the touch.
• A high-pressure line that feels cold indicates a pressure drop due to
an obstruction in the system such as a clogged fitting or a crushed
refrigerant line.
4-2
TOYOTA Technical Training
Diagnosis and Repair
Need for
Periodic
Maintenance
Periodic maintenance is required on all A/C systems. Ideally, a leak-free
system should keep running for many miles, but a variety of conditions
can cause the system to malfunction or to not operate at peak efficiency:
• Systems with conventional rubber hoses will suffer a gradual loss of
refrigerant. Moisture will also enter the system through these hoses
due to the porosity of the hose material. Both problems will be
aggravated by heavy A/C use in humid climates.
• Newer, nonpermeable hose materials reduce refrigerant loss through
rubber hoses. However, A/C systems still gain moisture and gradually
lose refrigerant through the compressor shaft seal. During long periods
of system inactivity, the seals lose their oil coating and sealing ability.
• Water can enter the system and form weak solutions of hydrochloric
and hydrofluoric acids. These acids will wear out internal components
and may lead to pinhole leaks in the system.
• Normal wear and tear of moving parts inside the compressor and
expansion valve will reduce system efficiency and may clog small
passages in the system.
A/C-Specific
Maintenance and
Inspection
These situations may cause the system to not cool, and not show any
mechanical failure. Because of this, the A/C system requires periodic
maintenance to restore it to an efficient operating condition. Periodic
maintenance includes the following:
• Visually inspect the system for airflow restrictions, drive belt tension
and obvious component failure.
• Check system operating pressures to confirm low charge condition.
• Recover the refrigerant from the vehicle.
• Evacuate the system to remove any moisture.
• Partially charge and check the system for leaks.
• Repair any leaks as needed.
• Recharge the system and check its performance, including the fan
system.
• Remove any debris or dirt from condenser fin surfaces.
TOYOTA Air Conditioning and Climate Control – Course 752
4-3
Section 4
Diagnostic
Trouble Codes
(DTCs)
Automatic A/C systems use an electronic control unit to control the
refrigeration and the air distribution systems. To diagnose the system,
the A/C ECU provides several Diagnostic Trouble Codes (DTCs) to help
identify the malfunction. Periodic maintenance includes checking for
DTCs. An OBD II scan tool connected to the vehicle’s Data Link
Connector can also read DTCs in the system. In addition, the scan tool
may be able to check the operation of various A/C system actuators.
Chart of A/C DTCs
DTC No.
(See Page)
00
Detection Item
Normal
Room temperature sensor
1
11*
(05–470)
Ambient temperature sensor circuit
2
12*
(05–473)
Memory
—
—
• Room temp. sensor
• A/C amplifier (Heater Control Housing)
• Harness or connector between room temp. sensor and
A/C amplifier (Heater Control Housing)
O
(8.5 min. or more)
• Ambient temp. sensor
• Harness or connector between ambient temp. sensor
and A/C amplifier (Heater Control Housing)
• A/C amplifier (Heater Control Housing)
O
(8.5 min. or more)
Evaporator temperature sensor circuit
• Evaporator temp. sensor
• Harness or connector between evaporator temp. sensor
O
(8.5 min. or more)
and A/C amplifier (Heater Control Housing)
• A/C amplifier (Heater Control Housing)
Water temperature sensor circuit
• Harness or connector between ECM and A/C amplifier
(Heater Control Housing)
• ECM
• A/C amplifier (Heater Control Housing)
13
(05–475)
14
(05–478)
21
Trouble Area
Solar sensor circuit
–
O
(8.5 min. or more)
• Solar
Fig. 4-2
752f402
On some vehicles, the scan tool may not be able to retrieve DTCs in the
system. If this is the case, DTCs can be read by observing a blinking
pattern on the Malfunction Indicator Lamp (MIL) or by a display on
the A/C control panel. The procedure to access DTCs in this manner
is described in the Vehicle Repair Manual and in Section 7 of this
Student Handbook.
DTC Check on
A/C Control Panel
DTC
• Code appears on panel.
• Multiple codes flash
alternately.
Fig. 4-3
752f403
4-4
TOYOTA Technical Training
Diagnosis and Repair
Special Tools
Here are some special tools needed to service and test the A/C system:
Thermometer
• Thermometer – Essential to compare vent outlet temperature with
ambient (outside) temperatures during performance checks and for
checking system pressures.
A/C Pressure
Gauge
• A/C Pressure Gauge – Determines how much refrigerant is in the
system. It also provides a convenient location to attach other service
equipment to the system. The A/C pressure gauges can be part of a
Manifold Gauge Set or built into a Charging-Recovery Station. Two
gauges are connected to the system; one for the low-pressure side and
the other for the high-pressure side. The gauges and hoses follow a
standard color code. The low side is blue and the high side is red.
Each gauge shows the pressure in that part of the system.
When part of a Manifold Gauge Set, the valves (marked Low and High),
allow one or both inlets to connect to a central passage (thus the term
“manifold”). A third hose fitting is reserved for charging or evacuating the
system.
The center hose of a manifold gauge set connects to a refrigerant tank for
charging or to a vacuum pump for evacuating the system. Charging the
system must only be performed on the low-pressure (“suction”) side. This
prevents dangerous pressure from developing in the refrigerant supply tank.
A/C Pressure
Gauge Connection
Note: Pressure gauges
are built into the latest
recovery machines.
100
0
100
0
300
400
PSI
PSI
LO
HI
Fig. 4-4
752f404
The static charge (system pressure with system OFF) is also of value when
troubleshooting. The “rule of thumb” is a 1:1 ratio on the gauge reading;
approximately 1 psig for every 1° F of ambient temperature. Thus, on an
80° F day, the system should have approximately 80 psig static pressure.
Caution:
For your safety, ensure each hose is connected to the correct service port
in the system. On older CFC-12 systems, the two fittings may be the same
size: the high-side fitting is always a smaller diameter line, and the low-side
fitting is in a larger diameter line. If in doubt, consult the Vehicle Repair
Manual and carefully follow the refrigerant path to confirm each fitting.
TOYOTA Air Conditioning and Climate Control – Course 752
4-5
Section 4
The following chart describes the pressures in a fully charged system
given the ambient (existing) temperature in the test area. Because
humidity places a higher load on the A/C system, pressures will vary
within the range shown depending on the relative humidity. These
pressures also assume adequate airflow over the condenser: Position an
external fan to blow air through the front bumper opening, particularly
on rear-wheel drive vehicles with a belt-driven fan.
Normal
Refrigerant System
Pressures
Ambient
High Side
Temp ° F PSIG, HFC-134a
60
70
80
90
100
110
120-170
150-250
190-280
220-330
250-350
280-400
Low Side
PSIG, HFC-134a
High Side
PSIG, CFC-12
Low Side
PSIG, CFC-12
7-15
8-16
10-20
15-25
20-30
25-40
120-150
140-180
160-250
200-280
220-300
250-320
5-15
8-16
10-18
12-25
15-30
20-35
(These pressures are also listed in the Vehicle Repair Manual in metric
units of ° C and kg/cm2.)
It is normal for the gauge needles to fluctuate (change reading) as the
clutch cycles ON and OFF and the heat load changes, but they should
not swing wildly. In addition:
• If the test pressure is below the ranges indicated, this indicates an
undercharged system that cannot exchange heat efficiently.
• Normal low-side pressure along with a much greater than normal
high-side pressure indicates air in the system.
• When both pressures are above range, the system is overcharged or
insufficient air is flowing through the condenser.
• If both gauges show equal pressures in the 60-80 psig range, this
indicates a fully charged system with an inoperative compressor.
Additional conditions and specific component failures can be diagnosed
based on gauge readings as shown in the Vehicle Repair Manual.
• Correct refrigerant charge amount is listed both in the Vehicle Repair
Manual and on an underhood label, which also list the correct
compressor oil type.
4-6
TOYOTA Technical Training
Diagnosis and Repair
RecoveryRecyclingRecharging
Station
Recovery-Recycling-Recharging Station – A self-contained unit that
connects to the A/C system. This unit monitors system pressures as well
as recycles, evacuates and recharges the system with the correct amount
of refrigerant. These stations usually contain pressure gauges to connect
to and to monitor system pressures. There is additional information in
this section.
Recovery-RecyclingRecharging Station
• Refrigerant type specific
for CFC-12 or HFC-134a
systems.
• Used for recovery,
recycling, evacuation and
recharging.
Fig. 4-5
752f405
Leak Detection
Leak Detector – Low gauge readings usually indicate the system has a
leak. A small quantity of refrigerant in the system generally indicates a
small leak. However, the gauge can’t tell you where to locate the leak. A
simple visual inspection may reveal large leaks, especially those that result
from body damage. Oil stains are usually found around any refrigerant
leak. System fittings are the most likely sources of leaks.
When the leak is not obvious, a leak detector can be used to pinpoint the
source. Finding a leak this way requires some refrigerant in the system.
You can find a leak if the vehicle has high-side pressures greater than
60 psig. If system pressure is lower than this, add no more than one
pound of refrigerant to the system, then test. After leak testing, use the
recovery station to remove the refrigerant before opening the system for
repairs.
The most accurate way to find leaks is with an electronic leak detector.
Modern units can detect leaks as small as one ounce per year. The detector
contains an audible or visual signal to indicate a leak. Finding leaks with
a leak detector is a skill that requires patience and knowledge of the
principles of refrigerants.
TOYOTA Air Conditioning and Climate Control – Course 752
4-7
Section 4
Electronic
Leak Detector
Fig. 4-6
752f406
Here are some tips using a leak detector:
• Refrigerants are three to four times heavier than air. Thus, the leak
will be easiest to find below the leak source.
• Look for streaks of oil around suspected leak areas.
• Leaks on the high-pressure side may be easier to find when the system
is operating.
• Leaks on the low-pressure side may be easier to find when the system
is not running.
• Small leaks will be easier to detect when the system is OFF and no
fans are blowing air.
• After locating a suspected leak, use compressed air to blow residual
gas from the area.
• Many leak detectors do not sense at the tip, but rather inside the unit.
Allow time for the sampled air to be drawn into the unit by moving the
tip no faster than one inch per second.
• To check for refrigerant leaks in the evaporator, probe the evaporator
drain tube under the vehicle after clearing any mud or water from the
area. With the A/C system OFF, cycle the A/C blower motor ON briefly
to blow any refrigerant through the drain tube.
• To detect leaks inside the plenum (air distribution housing), switch the
fan OFF for a minute then click it ON momentarily to force any leaking
refrigerant gas to the outlet vents where the leak can be detected.
Older leak detection techniques rely on a torch flame that changes color
in the presence of CFC-12. Due to the danger of potential phosgene gas
poisoning, do not use this type of detector. Colored and ultraviolet dyes
have also been used, but there’s a danger of staining interior fabrics
using these dyes.
4-8
TOYOTA Technical Training
Diagnosis and Repair
Leak-Testing
Dyes
Toyota does not recommend using leak-testing dyes as their long-term
residual effects have not been fully tested. Some dyes lose their effectiveness
over time and leaks are not accurately detected once the product has dried
away from the leakage area. Leaks located within an evaporator case or in a
hard-to-see location may also go undetected and repeated applications of
dyes during repeated checks can raise the level of contamination of the
system lubricant with unknown adverse effects. Dyes are often injected
with a new charge of PAG oil. Repeated dye applications will result in “over
oiling” the system requiring thorough cleaning and flushing of the system.
System Sealant
(“Stop Leak”)
Products
Toyota does not recommend the use of A/C system sealants for minor
repair of leaks or as a preventative additive during system service.
Sealants may cause gumming of system passages and may even result in
magnetic clutch engagement problems if the leak is at the compressor
front seal. Warranty reimbursement could be denied if a subsequent
component failure is linked to the use of sealants in a Toyota system
(Denso®), the air conditioning supplier company, does not recommend
sealant products in the system. If not performed properly, flushing out
residual sealant gum may result in serious consequences.
Several charging station equipment manufacturers have stated that their
equipment is damaged by the use of both system sealant and refrigerant
dye products being present in the A/C system. Damage by contamination
is not included in the equipment warranty and cannot be repaired at the
dealership.
TOYOTA Air Conditioning and Climate Control – Course 752
4-9
Section 4
Refrigerant
Identifier
Refrigerant Identifier – Verifies the type of refrigerant in an A/C system.
Refrigerant supply and system cross contamination is unfortunately very
common in the industry. Unprofessional retrofitting, illegal top-offs and
unapproved drop-in replacement refrigerants can contaminate dealership
equipment and storage container supplies. Decontaminating equipment
can be very expensive. A good rule is to use the refrigerant identifier
equipment on every vehicle that enters your service department for A/C
service or testing even if your dealership originally retailed the vehicle.
It is also highly advisable to check every new supply container of
replacement refrigerant purchased before connecting it to your charge
station, regardless if you obtained it from a familiar source. Follow the
refrigerant identifier equipment manufacturer’s procedures and
recommendations on judging for cross contamination. Keep a “contaminated
refrigerant” container on hand that is well marked for the recovery and
disposal of contaminated refrigerant the identifier has detected. Keep
the above special contaminated refrigerant container separate from
noncontaminated supplies and dispose of it properly at an authorized
recycler when it is filled to capacity. Do not just release contaminated
refrigerants to the atmosphere. This is both harmful to the environment
and very costly if you are caught. Be sure you are certified to handle and
recycle refrigerants by an accredited association such as MACS or ASE.
Not being certified can be expensive in fines and loss of business.
Refrigerant
Identifier
Sample Exhaust Port,
on Rear of Case
Portable Case,
Bottom Half
• Prevents
cross-contamination.
• Detects air in system.
Control Panel
• Reads in %.
Power Cord
Sample Inlet
Port
Air Intake Port
System Pressure
Gauge
Purge Vent Port
Sample Filter
Printer Port
Fig. 4-7
752f407
4-10
TOYOTA Technical Training
Diagnosis and Repair
Drive Belt
Tension Gauge
Drive Belt Tension Gauge – Accurately measures the tension of
multiribbed belts. Multiribbed belts do not tolerate stretch as much as
V-belts.
• Insufficient tension will result in belt slippage.
• Excessive tension puts extreme loads on the front compressor shaft
bearing.
• There are different tension specs for new versus used belts.
• Serpentine drive belts drives may have a scale on an automatic belt
tensioner to indicate belt wear. If the arrow falls outside the scale area,
replace the belt.
Belt Tension
and Wear
Automatic tensioner belt wear range:
A = “Normal” range
B = New belt range
Miscellaneous
Special Tools
Manual tension
measurement with gauge
Fig. 4-8
752f408
• Hand Vacuum Pump – Used to test vacuum-operated devices.
• Torque Wrench – Along with adapters, a torque wrench is needed to
tighten fittings to the proper torque. A set of four, fixed preset, open-end
SST torque wrenches are available in the appropriate sizes.
• Quick Disconnect Tool – Removal tool to separate high and low
pressure refrigerant lines using a nonthreaded fitting. The tool frees
the clamp which allows the refrigerant lines to separate.
Quick
Disconnect Tool
Push
Pull
• For quick
disconnect fittings.
• Two sizes.
SST
Release Lever
TOYOTA Air Conditioning and Climate Control – Course 752
Fig. 4-9
752f409
4-11
Section 4
• Shaft Seal Protector Tool – Compressor shaft seals can be replaced if
they leak. This tool protects the shaft seal from tearing when installing
the compressor front housing over the compressor shaft threads.
Shaft Seal
Protector Tool
Used to protect
shaft seal when installing
front housing.
Fig. 4-10
752f410
• Front Seal Driver-Installer – This special tool allows easy removal of
the compressor shaft seal from the front housing. It is also used to
install the compressor seal.
Front Seal
Driver-Installer
SST
Fig. 4-11
752f411
4-12
TOYOTA Technical Training
Diagnosis and Repair
Resource
Materials
The Toyota Repair Manual for each vehicle is always the starting point for
diagnostic and service information.
Repair Manual
• Air conditioning and
heating section.
• Diagnostic section.
Fig. 4-12
752f412
The manual includes:
• Symptomatic troubleshooting charts
• Pressure gauge readings for various conditions
• Component locations and repair procedures
• Refrigerant charge quantity and oil quantity for component replacement
Toyota Electrical Wiring Diagrams (EWDs) also are needed to diagnose and
repair. They contain location diagrams and testing specifications for
electrical components.
EWD Manual
• System schematics
and power circuits.
• Connector locations.
• Ground locations.
Fig. 4-13
752f413
TOYOTA Air Conditioning and Climate Control – Course 752
4-13
Section 4
Troubleshooting,
Service and
Repair Tips
A variety of maintenance conditions can affect the A/C system that may
not be revealed by standard diagnostic procedures.
• If a system does not blow sufficient air, check for obstructions of the
fresh air intake or body exhauster vents outside the vehicle.
• Restricted (clogged) fresh air filter behind glove box needs replacement.
• The expansion valve may fail in the open mode as a result of debris in
the system (perhaps from a past malfunction). The expansion valve can
also seize in the closed position due to a loss of lubricant. Apparent
expansion valve failure may simply be a case of the capillary tube
(“sensing bulb”) not being in contact with the evaporator outlet line.
• Paper, leaves and mud can clog the condenser fins. This reduces
system performance and can cause overheating and a blown fusible
plug or relief valve. The debris can often be blown out with compressed
air or a water hose. If necessary, special “combs” are available to
straighten bent condenser fins.
Clearing
Condenser
Obstructions
Bugs or dirt will increase
system pressures and
reduce cooling efficiency.
Fig. 4-14
752f414
• A system which does not produce cool air or blows a visible mist
(even though the fan works) may have one of two malfunctions:*
1. An iced evaporator. This can be caused by using MAX cooling with
a low fan speed or a failure in the thermistor/amplifier unit (to be
discussed in A/C controls).
2. The evaporator drain hose may be clogged with leaves or mud
which will cause the evaporator housing to fill with ice and water.
This will restrict airflow. A wet carpet is one symptom of a clogged
evaporator drainline.
* Some mist or fog can normally occur on humid days when the
system is first switched ON.
• A simple way to check the operation of the electric fan system is to
unplug the coolant temperature switch or refrigerant pressure switch
while the ignition is ON. This will result in the fans running at HIGH
speed.
Note:
4-14
Some models may require using a jumper wire to test operation, see W/D.
TOYOTA Technical Training
Diagnosis and Repair
• Every system will slowly lose refrigerant through the front compressor
seal, especially if the system is unused for long periods and the lip seal
dries out. It is not unusual to lose half a pound each year. At this rate,
the system will lose its effectiveness in two to three years. This slow
leak will not be apparent during normal maintenance and is too small
to be detected with a leak checker.
• A system that loses more than half a pound per year has a real leak.
Leaking front seals may be easy to diagnose due to the oil stains on
the clutch and in front of the compressor. The seal is easily replaced
and on some models it can be done without removing the compressor.
When handling the front seal, always coat your fingers in oil to prevent
body oils and acids from etching the delicate sealing surface.
Recover any refrigerant remaining in the system before removing the seal.
Compressor Seals
O-Rings
Lip Seal and Ring
Component
Replacement
O-Rings
Fig. 4-15
752f415
• Observe torque specifications. On threaded fittings, use two wrenches.
Hold the male fitting stationary with a wrench while rotating the
female fitting (nut). Use a torque wrench for final tightening.
• Always handle O-rings carefully. Handle with oil-covered fingers or
with a toothpick.
• Always install the receiver-drier last. Keep it sealed until the last
moment to prevent the desiccant from absorbing moisture. It will
become totally saturated with 10 minutes of exposure to humid air.
TOYOTA Air Conditioning and Climate Control – Course 752
4-15
Section 4
Refrigerant
Recovery
• Old system refrigerant must be recovered before any repair requires
opening the A/C system.
• Always start by connecting a manifold gauge set to the service fittings.
• Carefully measure the oil removed from the vehicle with the recovery
machine.
Minimum
Evacuation Time
Flushing
Precautions
Evacuation Process
Evacuation
Airtight
Check
30 minutes
or more
Leave for
5 minutes
Top-Up Charging
of Refrigerant
Refrigerant
Leak Check
Charging
Refrigerant
Fig. 4-16
752f416
Flushing products and procedures are not recommended by Toyota, and
parts should be replaced if debris contamination is suspected. Flushing
does not always remove all debris trapped in the system. Remaining
debris can dislodge later and damage the compressor or block the
expansion valve. Flushing a system using CFC-12 or HFC-134a
refrigerant requires recovery of refrigerant used without allowing it to
escape into the atmosphere.
Aftermarket flushing products, while sometimes effective, may not be fully
tested to determine any long-term residual damage or corrosion to the
compressor, condenser, expansion valve, evaporator, hoses, seals or other
system components. Metal particles embedded in internal hose passages
cannot always be easily dislodged during flushing as they were forced
into the hose under high pressure. Debris within a “parallel flow-style”
condenser is very difficult to flush out as the flushing agent can just
bypass the debris. Flushing agents must be thoroughly removed from a
system to minimize any residual effects such as oil dilution, corrosion, or
other damage. Using refrigerant to flush requires recovery of all refrigerant
used in the process.
Evacuation
After completing repairs, evacuate the system to remove moisture. This is
important for system durability as moisture will form metal-destroying
acids and create ice blockage at the expansion valve. Evacuation means
applying a strong vacuum to the system. This has the effect of lowering
the boiling temperature of water which will boil out of the system
(vaporize) at room temperature. With a system vacuum of 29.5 inches
Hg at sea level, water will boil at 59° F (15° C).
A vacuum pump will create 29.5 inches of vacuum. The correction for
higher altitudes is to subtract one inch per 1,000 feet above sea level.
Connect the A/C service hoses to both service ports and evacuate for at
least 30 minutes before charging the system after repairs (newly installed
4-16
TOYOTA Technical Training
Diagnosis and Repair
systems = 10 minutes). This process will remove any moisture in the system.
However, this will not remove moisture from a saturated receiver-drier
which should be replaced.
After evacuation, close both valves on the manifold gauges set. Allow the
system to remain under vacuum for a few minutes as a final leak check
before charging.
Refrigerant
System
Lubrication
Mobile air-conditioning systems require lubrication for the compressor
and the expansion valve and to prevent corrosion inside the system. This
is supplied by a special lubricating oil which mixes with the refrigerant
and travels throughout the system.
The oil coats the inside of each component, lubricates the bearings, rings
and seals of the compressor and the moving parts of the expansion valve.
The oil carries debris to the filter inside the receiver-drier. Different oils
are formulated for the A/C system depending upon the type of compressor
design and refrigerant used. Use only the recommended lubricant as
specified in the Vehicle Repair Manual.
A/C System
Lubricating Oils
Compressor Type
Piston (reciprocating)
Scroll or Rotary
Through-Vane
Piston (reciprocating)
Scroll or Rotary
Through-Vane
Hybrid Electric
Delphi
Note:
Adding Oil
After Repairs
Note:
Refrigerant
CFC-12
HFC-134a
Recommended
Oil
Part Number
ND-6
07117-68040
ND-7
07177-68030
ND-8
08885-09107
ND-9
08885-09117
ND-11
RL-897
08885-09127
Do not mix different types of compressor oils together. Not all types are
compatible. Drain oil from the recovery/recycling machine after each
vehicle serviced.
When opening the A/C system for repairs, replace the correct quantity of
lubricating oil into the system. After replacing a large component, the
Vehicle Repair Manual specifies the exact amount of oil to recharge in
addition to the amount removed during the recovery process. When
replacing a compressor, remember that a new or remanufactured
compressor usually has enough oil to fill the entire system. Therefore, you
must compensate (add/remove) lubricant for the proper system amount.
Excess oil reduces the thermal efficiency of the system. The process of
leak checking with dyes adds even more oil into the system.
TOYOTA Air Conditioning and Climate Control – Course 752
4-17
Section 4
Refrigerant/Oil
Proportion
in System
• When replacing parts in
the system, some oil is
lost and must be added.
• Replacement
compressors have a full
system amount of oil.
Fig. 4-17
752f417
If no oil-retaining components are replaced, only add as much oil as was
removed during the recovery process.
Add lubricating oil to the system after evacuation and before charging.
Some charging stations include oil-charge capability, or a special bottle
can used to meter the oil removed by the evacuation process.
Inline Filters
Aftermarket inline filters are commonly available in the market, however,
they are not recommended by Toyota and certain precautions must be
kept in mind.
• Inline filters can restrict flow and lessen performance or raise
pressures in the system.
• Improperly installed or poor quality products can leak resulting in a
comeback and possible system damage due to leakage and lubricant
loss.
• Improperly installed or poor quality inline filters can fail over time
and block the inlet port to the compressor or cause internal physical
damage.
• Under-hood areas are limited in space and properly positioning a filter
may be difficult.
• System hoses and pipes should not be cut or otherwise modified to
prevent leakage or failure.
4-18
TOYOTA Technical Training
Diagnosis and Repair
Performance
Checking
The final step in a repair is to perform a final check of your work. This
final performance check should include:
• Recheck belt tension with the gauge.
• Start vehicle, switch A/C ON, then recheck system pressures.
• Measure the dash vent outlet temperature. It should be 35° – 45° F
depending on temperature and humidity conditions.
• Observe the operation of the electric cooling fans.
• Observe the operation of the idle up system.
Note:
When conducting a Performance Test, refer to the Repair Manual as to
conditions such as doors open or closed, engine speed and outlet register
temperatures. Actual temperatures will vary from the standard 35° – 45° F
outlet temperature depending on temperature and humidity levels.
In order to allow vehicle and tool manufacturers to develop universal
service equipment, there are principles and procedures for environmentally
sensitive A/C repair. These standards have been created by the SAE in
compliance with Section 609 of the Clean Air Act.
• Recovery refers to the containment of gases during use, processes
and service.
• Recycling refines used refrigerant from mobile A/C systems to a purity
standard for reuse.
• Reclamation refines used refrigerant from a variety of sources to a
stricter-than-new standard.
• Recharging refers to charging an A/C system with refrigerant.
• Underwriter’s Laboratories (UL) has developed testing procedures
used to certify that recovery/recycling equipment meets the standards
set by the SAE for automotive, light truck and RV use.
Recovery and
Recycling
Techniques
Recovery/recycling equipment all works essentially the same:
• Oil separation occurs in a heat exchanger and prevents hydraulic
locking of the recovery machine compressor.
• Moisture and acids are trapped in a large-volume replaceable desiccant
package.
• Inline filter (usually integrated with the desiccant) filters small particles
from the refrigerant.
• Moisture indicator warns that moisture content exceeds allowable
levels. This indicates the need to replace the desiccant.
• Noncondensable gases (air) settle by gravity to the top of the recovery
tank. A gauge indicates when the air quantity exceeds the maximum
and must be vented to the atmosphere.
TOYOTA Air Conditioning and Climate Control – Course 752
4-19
Section 4
Most recovery/recycling stations perform all these processes in a single
pass. With a one-pass machine, any recovered refrigerant in the storage
cylinder is recycled and immediately ready for reuse. Some machines do
not fully recycle during the recovery process. Two-pass machines operate
in a recycle mode only after recovering refrigerant from the vehicle.
Note:
Some recycling machines cannot identify the many different types of
refrigerant gases that are on the market. It is important to never mix
refrigerants in a single machine.
With various refrigerants being used in the aftermarket, it is important to
use a refrigerant identifier to verify it is safe to recharge or to recover
the refrigerant.
• Different refrigerants cannot be separated and may produce a mixture
that has different or unpredictable properties.
• Severe permanent damage to the recovery/recycling machine is likely
if an incompatible refrigerant is recycled.
Equipment
Operation
A/C System
Identification
All recovery/recycling equipment works about the same way in order to
meet SAE standards. Control locations may vary and some functions
which are automated on some machines may be manually operated on
others. Connection to the vehicle A/C system is always through a pressure
gauge set. The gauge set may be part of the recovery/recycling station.
CFC-12 Service Fittings
Schraeder-type, all same size
HFC-134a Service Fittings
SAE. Different sizes for High and
Low pressure
High-pressure: Smaller OD/Red
Low-pressure: Larger OD/Blue
Noncondensables
With a one-pass machine, recycling is only necessary if the tank has been
contaminated with excessive noncondensables or if the desiccant/filter
is saturated.
At room temperature, refrigerant can be compressed or condensed into a
liquid state. Air cannot. Noncondensables refer to gases in the recycling
system that will not condense into a liquid. It is normal to see some
amount of noncondensable gases after recycling. When the recycling
process is complete, liquid refrigerant in the storage cylinder will settle to
the bottom of the tank and any air will rise to the top where it can be
vented from the PURGE fitting.
4-20
TOYOTA Technical Training
Diagnosis and Repair
Based on the pressure/temperature characteristics of refrigerants versus
air, a simple measurement can determine the presence of noncondensables
in a room-temperature cylinder that has not been disturbed for at least
12 hours.
1. Measure the exact ambient temperature within 4 inches of the cylinder.
2. Measure the pressure of the gas in the cylinder.
3. Find the point where your pressure and temperature intersect on the
chart:
• If the point is below the black line, the refrigerant is safe to use.
• If the point is above the black line, open the VENT or PURGE valve
until the pressure falls to below the limit shown in the chart.
Noncondensables
Chart
Safe Limit for Noncondensables
160
150
• Air is a noncondensable.
140
Pressure, psig
• Refer to text on this
page to use chart.
130
120
110
100
90
80
70
65
70
75
80
85
90
95 100 105 110 115
Temperature, Degrees F
Fig. 4-18
752f418
If the pressure cannot be brought within the limit shown, recycle the
entire contents of the cylinder. Only cylinders of completely recycled
refrigerant may be stored. Noncondensables may present a danger of
tank corrosion or bursting under extreme conditions.
Recycling stations may include a double-needle pressure gauge that
indicates noncondensables when the two needles are more than 10 psi
apart. The gauge is only accurate if the refrigerant has been undisturbed
for 12 hours. Some stations have an automatic purge function to vent
condensables.
A recovery/recycling machine that continually gives indications of moisture
or noncondensables should have a new filter-drier installed and then
checked for leaks.
TOYOTA Air Conditioning and Climate Control – Course 752
4-21
Section 4
Storage
Cylinders
Refrigerant cylinders (“tanks”) are designed to only hold a specific gas
and have unique fittings for each gas to prevent contamination.
• CFC-12 cylinders are white or off-white
• HFC-134a cylinders are pale blue
The U.S. Department of Transportation (DOT) has developed safety
standards for heavy-duty service cylinders that may be charged with
recycled refrigerant. They are made of very thick gauge steel, painted on
the inside for corrosion protection and include an over-pressure safety
vent. These cylinders must be returned to the manufacturer for testing
every five years. They are always marked with “DOT 4BA” or “DOT 4BW,”
the date of manufacture and the maximum allowable content weight
(WC-XX).
Service cylinders have three fittings:
1. Liquid fitting with a blue shut-off valve connects to a siphon tube that
draws refrigerant from the bottom of the cylinder.
2. Gas fitting has a red valve and is connected to the top of the tank to
add or remove gas from the cylinder.
3. Vent fitting without a control valve allows venting of noncondensables
from the top of the tank.
Cap all fittings to prevent leakage when the cylinder is not used. New
service cylinders are shipped with a charge of pure nitrogen. This must
be vented to the atmosphere before using. Empty or new cylinders must
be evacuated for at least five minutes before using to maintain refrigerant
purity.
New refrigerant is shipped in disposable tanks of various sizes. These
tanks should not be refilled or transported without proper packaging.
Disposable tanks should only be filled with absolutely pure (“virgin”)
refrigerant which meets extremely tight tolerances for moisture and
noncondensable content.
Disposable cylinders have a single fitting connected to the top of the
tank. Most charging stations work best with liquid refrigerant so the tank
must mount upside down to place the fitting at the bottom. When a
disposable container is empty:
• Recover any remaining gases into a recovery/recycling station.
• Close the service valve on the cylinder.
• Mark the cylinder “EMPTY” and dispose properly.
4-22
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 4-1 (ON-CAR)
Refrigerant Identification
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
After completing this worksheet you will be able to accurately operate the Neutronics Refrigerant Tester which
will allow you to identify contaminants in refrigerants.
Background:
Identifying the refrigerant type prevents storage contamination and potential damage to the A/C
system and to recharging and recycling equipment.
Tools and Equipment:
•
Neutronics Diagnostic Tool
•
Toyota Vehicle
•
Safety Equipment
Sample Exhaust Port –
on Rear of Case
Portable Case –
Bottom Half
Section 1
1. Open the Neutronics Case and inspect the sample filter for discoloration or red spots anywhere on the
outside diameter of the filter element. If any problems are found with this filter it must be replaced.
2. Select the HFC-134a sample hose from the storage panel in the case cover. Install the sample hose onto the
inlet port of the test instrument (Finger tighten only).
3. Inspect the air intake port, the sample exhaust port, and the case vent ports for any obstructions.
TOYOTA Technical Training
4W1-1
Worksheet 4-1
4. Verify that the purge vent cap is securely installed onto the port.
5. Locate and identify the low-pressure fitting on the test vehicle.
NOTE: Do not connect the identifier to the vehicle yet.
6. Connect the power cord to 110 VAC and wait. The system display should read, “Cold.”
7. During the warm-up period, the system allows the operator to change the local elevation calibration.
8. To change the elevation setting on the tester, Press the “A” and “B” buttons simultaneously. The display
should read “ELE,” then a number. This is the factory setting. Press the “A” and “B” buttons separately to
increase or decrease the elevation setting.
DELUXE REFRIGERANT DIAGNOSTIC TOOL
9. Once the correct elevation is set, allow the instrument to sit for 20 seconds and the elevation value will be
accepted. The tester will return to the warm-up cycle.
10. After the warm-up cycle the tester will self calibrate at which time the display will read:
“READY:CON.HOSE, PRESS A TO START” — the green LED will be flashing.
11. Connect the service end of the test hose to the low-pressure service fitting, then open the valve.
12. Check the pressure on the tester gauge. It should read approximately 10 psig.
13. Press the “A” button to begin testing.
Note: For optimal results it is recommended that the tester be allowed to run an additional five minutes
during the warm-up cycle before pressing the “A” button to begin the test. This additional time allows the
instrument to stabilize.
14. The tester display should read, “GAS SAMPLING IN PROGRESS.”
4W1-2
TOYOTA Technical Training
REFRIGERANT IDENTIFICATION
15. Once the sampling is complete, the unit will display the results.
a.
If a printer is connected, press the “A” button to print the results.
b. Press the “B” button to exit if no air is present or to purge any air present in the system.
c.
Record your test results in the form below:
Printout from unit parallel port
Note: This printout can be obtained if you have access to a printer with a parallel port. It is useful
when contaminated refrigerant is found in a customer vehicle and proof is required.
Section 2
Air Purging Operation
16. If the test unit determines that there is air in the system the unit will prompt the operator. At this point,
press “A” to begin system purging and “B” to cancel purging.
17. Adjust the purge limit by pressing “B” when prompted by the equipment display. Pressing “A” or “B” adjusts
the purge limit up or down, respectively.
18. After reaching the desired purge limit, allow the system to adjust for 15 seconds without pressing any
buttons.
19. The test equipment will automatically store the purge setting.
TOYOTA Technical Training
4W1-3
Worksheet 4-1
Purge Cycle
20. When the tester is ready to purge you will see the message, “REMOVE PURGE CAP, CON. HOSE, PRS.A.”
21. Remove the purge cap from the purge vent port.
22. Install the purge vent hose onto the vent and point the free end of the hose away from the tester.
23. After connecting the hose, press the “A” button to begin the process.
24. The display will read, “NOW AIR IS XX.X%, PURGING TO XX.X%.” Purge times will vary depending on
applications. For example, a 50-pound storage cylinder that is 50 percent liquid will require approximately
one hour to purge. The purge process can be stopped at any time by pressing buttons “A” and “B”
simultaneously.
25. When the process is complete the display will read, “DONE, AIR IS X.X%. PRESS ‘B’ TO EXIT.”
The green LED will flash.
Error Codes
26. Refer to the manufacturer’s operating manual to describe the meaning of the following error codes:
ERR.1 ________________________________________________________________________________.
ERR.2 ________________________________________________________________________________.
ERR.3 ________________________________________________________________________________.
27. Return the station to its original condition.
Instructor Sign Off: ______________________________________
4W1-4
TOYOTA Technical Training
REFRIGERANT IDENTIFICATION
Refrigerant Identification
Name: ___________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 4-1 using the Refrigerant Identification worksheet in the classroom. Ask the instructor if
you have any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
Purpose of Refrigerant Identification
Set up and calibration
Connecting hose to vehicle
Reading % HFC-134a
Reading % air
Air purging
TOYOTA Technical Training
4W1-5
Worksheet 4-1
Notes
4W1-6
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 4-2 (ON-CAR)
Touch and Feel Diagnosis
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
Given this worksheet and a Toyota vehicle, you will evaluate a HVAC system by touching various components
and checking component temperatures.
Background:
The high- and low-pressure sides of the HVAC system provide distinct temperature differences. You can get a
pretty good idea of the performance of an A/C system by observing the temperatures of the various lines and
components. Knowing these differences can help you verify system operation and diagnose malfunctions in the
A/C system.
Tools and Equipment:
• This worksheet
•
Toyota vehicle
1. In the following illustration, the areas in blue are typically much cooler than those in red. What is the basic
reason for this difference?
________________________________________________________________________________________________
________________________________________________________________________________________________.
Note: Sub-cool Condenser
models have filter-drier built
into the Modulator portion of
condenser end tank.
TOYOTA Technical Training
4W2-1
Worksheet 4-2
2. A sight glass in the A/C system, while not as accurate as pressure gauge readings, can indicate if the
system is fully ___________________________.
Note: The sight glass is not used as much because it is no longer an accurate indicator of the correct
amount of refrigerant in the system.
3. Start engine and bring to operating temperature, then switch the A/C system ON.
4. Wait a few minutes, then touch all the refrigerant lines on the low side of the system.
They should feel ___________________________.
CAUTION: Observe personal safety. Be careful of rotating engine parts.
5. Describe the temperature of the refrigerant line leading from the compressor to the condenser.
_____________________________________.
Note: If the low- and high-side temperatures are okay, then the compressor is operating normally.
6. Using the A/C switch on the control panel, cycle the compressor ON and OFF and verify the compressor
clutch is engaging and disengaging.
A/C switch ON and compressor clutch engaged: Yes / No
A/C switch OFF and compressor clutch disengaged: Yes / No
7. In a normal operating system, the receiver-drier should feel
____________________________________ to the touch.
8. What is your diagnosis if a receiver-drier is cool to the touch on the expansion valve side of the component?
________________________________________________________________________________________________.
9. Diagnose this vehicle:
The A/C system is not cooling properly. There is frost on the expansion valve and on the line leading to the
expansion valve. What is your diagnosis?
________________________________________________________________________________________________.
Vehicle Interior
Performance Test
10. Adjust the temperature setting on the control panel to maximum cooling and full recirculation. Set the blower
speed to “High” and close all the doors and windows.
11. Insert a thermometer into the center vent and measure the air temperature.
a. After a minute or two, record the reading. ________________ °F.
b. What temperature should it be? _________________ °F.
4W2-2
TOYOTA Technical Training
TOUCH AND FEEL DIAGNOSIS
12. Switch the blower speed to “Low” and record any changes in temperature.
____________________________________ (temperature may drop).
Why the temperature change?
________________________________________________________________________________________________.
13. Increase the engine speed to 1,500 rpm and record any change in the temperature.
____________________________________ (temperature may drop).
Why the temperature change?
________________________________________________________________________________________________.
Instructor Sign Off: ______________________________________
TOYOTA Technical Training
4W2-3
Worksheet 4-2
Notes
4W2-4
TOYOTA Technical Training
TOUCH AND FEEL DIAGNOSIS
Touch and Feel Diagnosis
Name: ___________________________________________________________ Date: _________________________
Review this sheet as you are completing Worksheet 4-2 for Touch and Feel Diagnosis. Check each category
after participating in the classroom discussion and completing the worksheet in the shop. Ask the instructor if
you have any questions regarding the topics provided below.
I have questions
Topic
I know I can
Comment
Low and high sides of system
Component identification
Location of sight glass
Sight glass appearance
Checking temperature output
Clutch cycling
TOYOTA Technical Training
4W2-5
Worksheet 4-2
Notes
4W2-6
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 4-3 (ON-BENCH)
Compressor Clutch Replacement
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
Given a Vehicle Repair Manual, this worksheet and other technical publications, you will correctly remove and
replace the A/C compressor clutch on a Toyota vehicle.
Background:
The compressor clutch is an electromagnetic device to connect the drive pulley to the compressor shaft. When
the shaft rotates, refrigerant circulates through the system.
Tools and Equipment:
•
Vehicle Repair Manual (TIS)
•
SST No. 07112-76060
•
SST No. 07112-211203
•
A/C compressor
•
Dial Indicator
•
Normal hand tools
Section 1
1. What page in the Vehicle Repair Manual describes the R&R procedure? ______________________
2. Approximately how much torque will it take to remove the shaft bolt? ______________________
3. Is the pressure plate shimmed? __________________________________________
4. What kind of hammer is suggested to remove the pressure plate from the shaft?
___________________________________________________________________________
5. After removing the pressure plate, there is a connector
mounted to one part of the unit in the following illustration.
What is the name of the part this connector is attached to?
_____________________________________
TOYOTA Technical Training
4W3-1
Worksheet 4-3
6. Remove all parts from the compressor shaft.
7. How many “Snap Rings” are there to be removed in the complete process? _________________
Reassemble Clutch
8. What direction (up or down) should the beveled side of the snap ring face? _________________
9. Reassemble the components onto the compressor shaft.
10. Set up the dial indicator to inspect the magnetic clutch.
11. What is the “Standard Clearance” between the clutch and pressure plate?
__________________________________________________________________________________
12. List the available shim sizes to adjust the gap:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
What is your measurement results? ______________________________
13. What page in the Vehicle Repair Manual did you find this information? ______________________________
Answer the following diagnostic questions based on the information in your Vehicle Repair Manual and
the Reference section in your Technician Handbook.
4W3-2
TOYOTA Technical Training
COMPRESSOR CLUTCH REPLACEMENT
14. There is an attempt to energize the A/C compressor. After switching the A/C ON, the clutch does not
engage. In addition, the compressor clutch does not produce a “clicking” sound. What two items would you
check first?
______________________
_______________________
15. You have confirmed source voltage to the compressor connector and decide to check the resistance of the
stator. What is the resistance specification for the stator?
_____________________________________________________________________________
16. If there is no source voltage at the stator connector and the stator resistance is okay, jump the connector to
the coil to bypass the _________________________________________.
17. After “jumpering” (bypass the A/C switch), the compressor clutch engages and the compressor runs quietly.
What is a reasonable conclusion based on these findings?
____________________________________________________________________________
18. What is a reasonable timeframe to run this compressor (circuit bypassed) for testing purposes?
________________________________________________________________________________________________
19. Explain the reason for your answer in #18.
_________________________________________________________________________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
Instructor Sign Off: ______________________________________
TOYOTA Technical Training
4W3-3
Worksheet 4-3
Notes
4W3-4
TOYOTA Technical Training
COMPRESSOR CLUTCH REPLACEMENT
Compressor Clutch Replacement
Name: ___________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 4-3 using the Compressor Clutch Replacement worksheet in the shop. Ask the instructor
if you have any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
Purpose of clutch shims
Identification of compressor
clutch parts
Removing clutch using SSTs
Dial Indicator set-up
Clutch gap and shim thickness
Clutch coil resistance
TOYOTA Technical Training
4W3-5
Worksheet 4-3
Notes
4W3-6
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 4-4 (ON-CAR)
HFC-134a Recovery
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
Given this worksheet, a Toyota vehicle, a Vehicle Repair Manual and a Refrigerant Recovery Machine, you will
operate the A/C recovery/recharging machines available at this station.
Background:
The setup and use of recovery and recycling machines will vary from dealership to dealership. This worksheet
emphasizes the importance of proper preparation and equipment safety issues. It is important to understand the
operation differences for each machine. Proper care and maintenance of any machine will prevent comebacks
and increase customer satisfaction. One person at your dealership should be responsible for maintaining the
recycling and recovery equipment.
Tools and Equipment:
•
Toyota Vehicle
•
Vehicle Repair Manual
•
Refrigerant Recovery Equipment
•
Safety Glasses
Section 1
1. Identify the make and model of the HFC-134a recycling/recovery machine at this station.
Brand _____________________________________ Model _______________________________________
2. Check the oil level in the vacuum pump assembly.
________Okay
3. When a new tank is placed into service, a small amount of refrigerant must be added to the new tank.
Approximately how much refrigerant should be added before using the new tank?
________________________________________________________________________________________________
Note: All of the above setup procedures have been performed for you.
4. Drain the oil catch bottle before recovery. Where is the oil catch bottle?
_________________________________________________________________________
__________ Done
Note: Verify that the oil catch bottle is empty. Place it back into its holder before starting.
TOYOTA Technical Training
4W4-1
Worksheet 4-4
5. Locate and identify the low-side and high-side A/C system fittings in the vehicle. Connect the appropriate
HFC-134a hose fittings to these ports.
__________ Done
Section 2
Recovery Procedures:
Note: Always check the A/C system with a refrigerant identifier test before recovery.
Verify there is sufficient refrigerant in the supply tank.
6. Check the sight glass or moisture indicator color on the recovery machine to determine if there is excessive
moisture in the system. If the machine has a moisture indicator:
Dry ______
Wet ______ (Check one)
If wet, notify your instructor to change the filter
7. Check the vacuum pump oil level
Okay / Not Okay (Circle one)
8. Engine OFF
9. Locate and record the following information from the A/C label in the engine compartment:
a. Charge amount: _________ lb.
b. Lubrication type: _________
10. What is the ambient temperature? _________ °F
4W4-2
TOYOTA Technical Training
HFC-134A RECOVERY
11. Connect the high- and low-pressure hoses from the recovery machine onto the vehicle.
Note: Verify the fitting valves are closed before connecting to the vehicle A/C system valves.
12. Before starting the recovery process, determine system performance as follows:
a.
Start engine and warm up to operating temperature. Set the system to maximum cold, then check the
temperature at the center vent.
What is the temperature of the system? __________________________
Note: See TIS for Engine Speed and vehicle door opening position.
b. Is this temperature an acceptable level of performance?
c.
Yes / No (Circle one)
Observe and record the refrigerant pressures on both gauges. The following illustration shows “normal”
gauge readings.
Low-pressure gauge ________ psi (21-35)
High-pressure gauge ________ psi (190-220)
TOYOTA Technical Training
4W4-3
Worksheet 4-4
d. Is this vehicle operating normally?
e.
Yes / No (Circle one)
What is your diagnosis of this system at this point?
________________________________________________________________________.
13. Follow the directions in the Equipment Operating Manual and recover the refrigerant from this vehicle.
Note: Verify the refrigerant valves on the recovery machine are closed.
Do not disturb the recovery machine or the refrigerant supply tank during the
recovery/recycling/recharging operation as this could upset the charge amount.
_______ Done
14. How much refrigerant did you recover? _______________________________________.
15. How does this compare with the amount on the label? _______________________________________________.
16. How much oil was removed during refrigerant recovery?” ____________________________________________.
What type and how much oil do you need to put back in the system? _________________________________.
Under what conditions do you add oil to the system during this procedure?_____________________________.
17. Remove moisture from the system with a vacuum pump. Evacuate at 29.5 in. Hg for approximately
5 minutes (See note).
________ Done
Note: If the system does not hold a vacuum there is a leak in the system.
This evacuation process is important. It normally takes 30-60 minutes to complete.
18. Does the system hold a vacuum after 5 minutes?
Yes / No (Circle one)
19. Follow the instructions for recharging and begin that process. Install the specified amount of refrigerant into
the system as you removed. Refer to the vehicle label or the Vehicle Repair Manual for the proper amount.
How much refrigerant are you going to charge? ______________________________.
20. Do the A/C Pressure Gauges display approximately the same amount when you started?
________ Done
21. Return the workstation to its original condition.
Instructor Sign Off: ______________________________________
4W4-4
TOYOTA Technical Training
HFC-134A RECOVERY
HFC-134a Recovery
Name: ___________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 4-4 using the HFC-134a Recovery worksheet in the shop. Ask the instructor if you have
any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
Importance of Refrigerant Recovery
Identification of parts of
recovery station
Location of vacuum pump and oil level
Low- and high-pressure hoses and
control valves
Location and use of oil drain bottle and
replenishment of oil
Recovery process from vehicle
Evacuation process
Recharging refrigerant to vehicle
Recovering charge station hoses
after use
TOYOTA Technical Training
4W4-5
Worksheet 4-4
Notes
4W4-6
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 4-5 (ON-CAR/IN-CLASS)
TIS Information/Leak Check
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
Use this worksheet as a guide to search for information on the TIS and use that information to check for
refrigerant leaks in a Toyota vehicle.
Background:
Refrigerant loss decreases the efficiency of the A/C system. A leak test will help determine the
location of the leak.
Tools and Equipment:
•
Vehicle Repair Manual
•
TIS Machine
•
Leak Detector
Section 1:
1. Access the TIS main screen menu.
2. Select “All Models” and “All Years.”
3. Select “Service Bulletins,” then “Search.”
4. Select “Heating and Air Conditioning,” then “Find.”
5. Select and print the following TSBs:
AC95-001
TOYOTA Technical Training
AC001-04
4W5-1
Worksheet 4-5
Section 2 (On-Car)
6. Use TSB AC95-001 to perform a refrigerant leak check on a vehicle. Before beginning, take the leak detector
to the Recovery/Recycling Machine and check it for leaks.
Leak check performed per TSB AC95-001: ________
7. List problems you discover as you complete the TSB concerning this type of leak detection.
_________________________________________________________________________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
8. Leak detection methods have been controversial since the appearance of various recycling machines. List
the problems regarding other types of leak detection.
Leak Detection Type
Disadvantages
Dye in refrigerant
Flame tester
Section 3 (In-Class)
9. Refer to AC001-04 and answer the following questions:
a.
Which new parts are to be installed for this countermeasure?
_____________________________________________________________________________________________
b. What parts should you inspect for trapped metal particles or debris?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
c.
How much compressor oil must be added or removed from the system when performing this
countermeasure procedure on a vehicle with dual A/C? _________________________________________
d. What type of compressor oil is used? _________________________________________
e.
If the compressor is replaced again in the future after this TSB procedure, how much compressor oil will
be required? ________________________________________________________________
Instructor Sign Off: ______________________________________
4W5-2
TOYOTA Technical Training
TIS INFORMATION/LEAK CHECK
TIS Information/Leak Check
Name: ___________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 4-5 using the TIS Information/Leak Check worksheet in the shop. Ask the instructor if
you have any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
Purpose of TIS terminal
Locating TSB on leak checking
Using the leak detector
Modifications to Sequoia A/C system
Determining correct amount of
compressor oil
TOYOTA Technical Training
4W5-3
Worksheet 4-5
Notes
4W5-4
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 4-6 (IN-CLASS)
A/C Pressure Gauge Diagnosis
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
Given the Technician Handbook and TIS you will evaluate and diagnose a simulated manifold gauge condition.
Background:
The A/C pressure gauges provide a snapshot of the operating condition of the A/C system. These readings can
help diagnose malfunctions in the system.
Tools and Equipment:
•
None
1. What are typical high-pressure and low-pressure gauge readings?
Low__________________psi
High__________________psi
NOTE: As you review the following gauge readings, keep in mind the operating conditions of the system and
why these conditions cause these gauge readings.
2. Observe the following pressure gauge reading
(assume ambient temperature is 80°F):
Low: Between 21-35 psi
High: Between 190-220 psi
What is the condition of the system? (See Normal System Refrigerant Pressure chart in
Student Handbook, Section 4). ___________________________________________________
TOYOTA Technical Training
4W6-1
Worksheet 4-6
3. The customer complains of poor cooling or no cooling at all and both pressure gauges are low.
What is your diagnosis? ___________________________________________________________________________
4. The customer complains of poor or no cooling.
What is your diagnosis? ___________________________________________________________________________
Here are the symptoms:
• Low-side
pressure is too high
• High-side
pressure is too low
• Gauge needles bounce
or erratic
4W6-2
TOYOTA Technical Training
A/C PRESSURE GAUGE DIAGNOSIS
5. What is the system condition in this example?
_________________________________________________________________________________________________
Hint: Gauge needles are erratic and cooling is periodic.
6. In this example, both pressures are high. What are two likely causes?
Symptom #1: ____________________________________________________________
Symptom #2: ____________________________________________________________
Hint: Different components are involved.
Here are the symptoms:
• Low-side
pressure is too high
• High-side
pressure is too high
• No bubbles are visible in
the sight glass
TOYOTA Technical Training
4W6-3
Worksheet 4-6
7. Describe how the above gauge readings might be related to a previous ineffective repair.
8. The following gauge readings are most common. The refrigerant level is to specification. The complaint is
poor or no cooling.
Condition: _________________________________________________________________
9. Explain the conditions of the problem in question #8.
Summary:
As shown in these examples, there are logical reasons for certain gauge readings. However, there are some
readings caused by more than one component or situation. Through the process of elimination, the components
can be tested to determine the cause of the malfunction.
4W6-4
TOYOTA Technical Training
A/C PRESSURE GAUGE DIAGNOSIS
Review Questions:
Fill in the blanks in the following statements:
1.
The low-pressure side sometimes draws a vacuum. List some reasons to explain this:
___________________________________________________________________________
___________________________________________________________________________
2.
The low-side pressure is high. List three causes:
a. ________________________________________________________________________
b. ________________________________________________________________________
c. ________________________________________________________________________
3.
The high-side pressures are abnormally high. List three causes:
a. ________________________________________________________________________
b. ________________________________________________________________________
c. ________________________________________________________________________
4.
What are normal pressures in an A/C system?
Low side: ___________________________ psi
High side: ___________________________ psi
Instructor Sign Off: ______________________________________
TOYOTA Technical Training
4W6-5
Worksheet 4-6
Notes
4W6-6
TOYOTA Technical Training
A/C PRESSURE GAUGE DIAGNOSIS
A/C Pressure Gauge Diagnosis
Name: ___________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 4-6 using the A/C Pressure Gauge Diagnosis worksheet in the shop. Ask the instructor if
you have any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
Identification of low and high side
Connecting the gauges low and
high side
Identify normal gauge readings
Identify low- or high-gauge readings
Identify moisture in system
Identify possible damaged compressor
TOYOTA Technical Training
4W6-7
Worksheet 4-6
Notes
4W6-8
TOYOTA Technical Training
Section 5
A/C System Controls
Lesson
Objectives
1. Locate and verify the operation of the air inlet control system.
2. Locate and verify the operation of the temperature control system.
3. Locate and verify the operation of the air distribution control system.
TOYOTA Air Conditioning and Climate Control – Course 752
Section 5
A/C System Controls
Temperature
Control
The heating, ventilation and air-conditioning system depends on the
engine as a source of heat and energy to drive the system that removes
the heat. The combustion process supplies the heat needed to warm the
vehicle interior. The engine’s output powers the A/C compressor to cool
the vehicle interior.
At normal operating temperatures, the engine coolant is about 220° F
(105° C) due to the cooling system pressure cap, thermostat and the
engine cooling fan. When the system is ON, the A/C evaporator operates
at a constant temperature of 32° F (0° C) based on the characteristics
of the refrigerant. Beyond this, there are driver controls to regulate the
amount of heat added to or from the interior in order to achieve a
comfortable interior temperature.
Temperature
Control System
Airflow Mode
Control
Air Inlet Control
Main controls in system.
Blower Speed
Control
Temperature
Control
Compressor
Control
Fig. 5-1
752f501
Heater
Control Valve
In simple systems, the heater control valve may be the only adjustable
temperature control. It controls the flow of hot coolant through the heater
core (heat exchanger) to increase the air temperature going to the interior.
Function of Heater
Control Valve
• Allows hot coolant into
heater core.
Heater Core
Heated Air
Airflow
• Normally only closed at
maximum cold setting.
Heater Control Valve
Fig. 5-2
Out
In
TOYOTA Air Conditioning and Climate Control – Course 752
752f502
5-1
Section 5
A cable-operated lever on the heater control valve controls the flow of
hot coolant through the heater core. On current Toyota vehicles, the valve
is completely closed when the system requires maximum cool air. At
all other times, the heater valve is fully open. Heat to the interior is
controlled by controlling air flow.
Cable-Operated
Heater Control
Valve
• Operated by
temperature control
knob or lever.
Rotary Valve
OUT
• Cable adjustment
is important.
IN
Fig. 5-3
752f503
The heater control valve controls the flow of hot coolant into the heater core
and opens in steps when the set temperature knob or slider moves from the
MAX COLD setting to a warmer setting. A misadjusted heater control valve
can result in reduced heating if it doesn’t open fully or will cool poorly if it’s
not fully closed.
Heater control valves respond slowly to changes due to the thermal
inertia of liquids, that is, the resistance of the coolant in the heater core
to temperature changes. The Heater control valve is usually open during
A/C operation except at coldest temperature settings (67° F or below).
5-2
TOYOTA Technical Training
A/C System Controls
Air Mix
Temperature
Control
Air is more responsive to temperature changes than a liquid. To take
advantage of this, some current air-distribution systems continuously
circulate hot coolant through the heater core. In this type of system, when
heat is needed, a controlled amount of air is allowed to pass through the
heater core. The heated air mixes with unheated air that bypasses the
heater core to achieve a comfortable mix. Since air has much less thermal
inertia than liquid, this system provides a very responsive, yet stable
adjustment of the air temperature.
Air Mix Control Damper
Air Mix
Temperature
Control
Damper is moved by
cable or electric
servo-motor.
Fig. 5-4
Heater Core
752f504
A movable door or damper called the blend door inside the blower
housing controls the air through and around the heater core and/or
A/C evaporator. The amount of air mix is controlled by either a cable or
a variable vacuum signal from a control panel.
Toyota vehicles use an electric motor to control the blend door. The air mix
servo-motor thus regulates the temperature depending on a variable
signal from an electric control (variable resistor) or by a signal generated
by another device. Additional information on servo-motors is in Section 6.
Air Mix Servo-Motor Control
Air Mix
Servo-Motor
DEF ON
• Moves air mix damper
or blend door.
OFF
• Also used for air
inlet damper.
FACE ON
–3
Fig. 5-6
–2
–0
–2
SW-TP (%)
–3
SW: Target Damper Opening Angle
TP: Actual Damper Opening
752f506
TOYOTA Air Conditioning and Climate Control – Course 752
Fig. 5-5
752f505
5-3
Section 5
The servo-motor may have an integral (built-in) variable resistor that
provides a signal to confirm the current position of the blend door. Later,
we will discuss why this function is important in automatic A/C systems.
Air mix temperature control systems still use a heater control valve, but it
is usually open under all conditions except maximum cooling. In other
words, the heater is at maximum hot unless the temperature control is
set to the coldest range.
Heater Core
Blend Door
• Shown in heat position.
Evaporator
• Dotted line is
cool position.
• Can be in between
or blended.
Blend Door
Fig. 5-6
752f506
Blower Speed
Control
Note:
The fan that circulates interior air is controlled by the driver to regulate
temperature and airflow. Fan speed is usually variable in steps by
controlling the source voltage to the fan motor through a series resistor.
When several resistors are connected in series, each resistor will drop
some portion of the total source voltage, and the total of all voltage drops
equals the source voltage.
Terminal 1 of the blower motor is supplied source voltage by the heater
relay whenever the blower switch is ON, but the motor connection to
ground passes through a string of resistors (typically three) called a series
resistor. The multiple position fan switch provides a connection to ground
from the various points in the series portion of the circuit. Increasing
resistance in the ground leg of the circuit limits current flow to reduce
fan speed while less resistance raises fan speed.
At low fan speeds, the blower switch does not provide a ground path. All
of the series resistors are used to reduce the source voltage to the motor.
At the HI speed position, the blower switch bypasses all of the resistors
to provide full source voltage to the motor.
Some vehicles have push buttons for fan speed selection instead of a
conventional rotary switch. The large size of a rotary switch means it can
handle the relatively high current of the blower fan circuit directly. With
smaller push buttons, a relay isolates the switches from the high current
fan circuit.
5-4
TOYOTA Technical Training
A/C System Controls
Blower Fan
Speed Circuit
40A
Heater
15A
Heater
• Blower resistor controls
fan speed.
• Blower motor current
controlled by fan
switches, blower control
relay and resistor.
Heater
Relay
Blower
Motor
Blower
Control
Relay
Junction
Connection
Blower
Resistor
Blower Fan Switch
Fig. 5-7
752f507
Typically, three or four speeds are available for blower fan operation
(depending on the number of elements in the series resistor). A specific
blower speed is provided for each switch position while the highest speed
bypasses the resistor.
Some late model vehicles use a large-diameter, small-width blower fan
and a compact, brushless blower motor. A built-in solid state control
circuit controls the blower motor speeds.
Old vs. New Style
Blower Motors
FET (Field Effect Transistor)
Brush
New type is brushless
with no blower resistor.
Motor
Control Circuit
New
Motor
Assembly
Fig. 5-8
Previous
TOYOTA Air Conditioning and Climate Control – Course 752
752f508
5-5
Section 5
Air
Distribution
Control
Manual A/C systems use servo-motors or cables to control the air
distribution and air flow. Many Toyota models have push-button, air
distribution selector switches. When pressed, the various switches send
signals to an amplifier (ECU) that controls the movement of the damper
doors with a servo-motor. Some Toyota vehicles may have touch-sensitive
air distribution controls on a screen display.
A/C Control Panel
Shown with all
segments illuminated.
Fig. 5-9
752f509
The air distribution system delivers air from the HVAC system to the
various parts of the interior. Fresh air first enters the vehicle at an air
inlet, usually at the base of the front windshield.
Control of Air
Distribution
Schematic
Heater
Evaporator
Inlet
Blend or mix doors
controlled by
servo-motors.
Blower Motor
FACE Vents
Fig. 5-10
752f510
Air Inlet Control
5-6
The air inlet control is a damper that is driver-controlled to allow fresh
air to enter (open) or to recirculate air in the interior (closed). The driver
has a choice of air inlet modes: FRESH or RECIRC (recirculated air). One
or two dampers positioned before the blower motor controls this mode.
TOYOTA Technical Training
A/C System Controls
FRESH
RECIRC
The fresh air intake mode allows maximum airflow through the vents
since the blower fan is assisted by vehicle speed. This mode is useful for
defogging windows in cold weather when outside humidity is lower than
that produced by vehicle occupants.
This mode allows the blower motor fan to recirculate the air from inside
the vehicle and provides maximum A/C performance since the air is
already “conditioned” (low temperature and humidity). This mode also
prevents foul outside odors from entering the vehicle. However, total airflow
is limited because the body air inlets are closed.
Newer vehicles may provide a blend of both modes for greater comfort
and windshield defrosting under most conditions. These vehicles may
typically switch to full recirculation when the system is set to the lowest
temperature (MAX COOL).
Many vehicles have a clean air filter located after the air inlet control
to deodorize and remove dust from the outside air. This filter must be
changed at specified intervals according to operating conditions.
Clean Air Filter
Clean Air Filter
• Behind glove box.
• Replacement interval in
Vehicle Owner’s Manual.
Fig. 5-11
752f511
At higher road speeds, airflow through the air inlet increases due to
aerodynamic forces. At lower vehicle speeds, the blower fan assists normal
airflow. From the blower fan, air passes through the evaporator, then
through or around the heater core before going to the plenum, the central
chamber inside the blower housing, then to the various ducts and air
outlets.
TOYOTA Air Conditioning and Climate Control – Course 752
5-7
Section 5
Air Distribution
Control and Air
Outlet Mode Chart
Note: Amount of airflow
from outlets in various
modes shown in
chart below and in
Vehicle Repair Manual.
Fig. 5-12
752f512
The size of the circle
indicates the proportion of airflow volume.
Air Outlet Mode
A
Center
Face
B
Side
Face
C
Rear
Face
FACE
D
Foot Defroster
–
BI-LEVEL
5-8
–
–
FOOT
–
–
FOOT/DEF
–
–
DEF
–
–
TOYOTA Technical Training
E
–
A/C System Controls
If the A/C is ON, the evaporator cools the air inside the plenum. The air
is then brought to the desired temperature by the position of the blend
door, the hot heater core and the air mix servo-motor. There are additional
damper doors (mode control dampers) that determine the distribution of
the treated air from the plenum into the passenger compartment. There
are usually three or more air outlets to the vehicle’s interior:
Distribution Mode
Air Direction, primary
Air Direction, secondary
DEF (Defrost)
Air flows to vents at base
of windshield
Foot level vents
HEAT
Air flows to foot vents
Defrost vents
BI-LEVEL
Air flows to both foot and
dash vents
–
FACE or VENT
Air flows to dash level vents
–
Typical mode settings. See Vehicle Repair Manual for specific settings.
Vehicle Repair Manuals describe specific air distribution patterns using
a chart (see sample charts). Notice that the larger circles indicate more
airflow than the smaller circles.
Air distribution to the desired air outlet duct is controlled by a switch on
the instrument panel. Some vehicles use a slide lever connected by a cable
to a variable-position damper. The damper doors can also be operated by
vacuum, supplied by a rotary vacuum switch on the instrument panel.
TOYOTA Air Conditioning and Climate Control – Course 752
5-9
Section 5
Typical Mode
Position Charts
Mode Position
Fig. 5-13
752f513
Damper Operation Chart (typical)
Control Damper
Air Inlet Control
Damper
Air Mix Damper
L/R Independent
Control
Control Position
A
Brings in fresh air
RECIRC
B
Recirculates inside air
MAX COLD – MAX HOT
TEMP SETTING
65° F (18° C) – 85° F (32° C)
E~D~C
E’ ~ D’ ~ C’
Varies the mixture ratio between fresh
and recirculated air to regulate temperature
F, K, L, O, R
Defrosts the windshield through the center
defroster, side defroster and side register
G, K, L, O, Q
Defrosts the windshield through the center
defroster, side defroster and side register
while air also blows from the front and rear
foot well register ducts
FOOT
H, K, L, O, P
Air blows out of the front and rear foot well
register duct and side register. In addition,
air blows out slightly from the center defroster
and side defroster
BI-LEVEL
I, J, M, N, P
Air blows out of the center registers, side
registers and foot well register ducts
FACE
I, J, M, N, R
Air blows out of the center registers and
side register
FOOT/DEF
5-10
Operation
FRESH
DEF
Mode Control
Damper
Damper Position
TOYOTA Technical Training
A/C System Controls
Dual-Plane
Air Distribution
Current vehicles may use an air-distribution system featuring a
dual-plane blower motor. This produces different airflow volume from a
single fan speed. The small and large fan blades circulate air through
different air distribution paths in the blower housing. This results in
more airflow to the FOOT vents than to the FACE vents.
Dual-Plane
HVAC Housing
Twin-bladed blower
motor provides different
air volume.
Expansion
Valve
Air Inlet
Servo-motor
Evaporator
Temp. Sensor
Air Outlet
Servo-motor
Clean Air
Filter
Dual-Plane
Blower Fan
Blower Pulse
Controller
Air Mix
Servo-motor
Evaporator
Heater Core
PTC Heater
(in Air Duct)
Fig. 5-14
752f514
TOYOTA Air Conditioning and Climate Control – Course 752
5-11
Section 5
This system also provides 2-way airflow in the vehicle. Under 2-way flow
operation, the system can introduce outside air and circulate internal air
at the same time. This allows warm RECIRC air to flow to the foot area
while dry, FRESH air flows to the upper area. The 2-way flow system
provides good heating and de-misting performance.
2-Way Airflow
Fresh, dry external air to the upper area
FRESH and RECIRC
combined airflow
External Air
Warm internal air to the footwell area
Fig. 5-15
752f515
A partition plate inside the A/C blower unit divides the airflow path
(external and internal passages). Thus, by controlling the external and
internal air doors separately, the vehicle has the following FRESH and
RECIRC airflow modes:
• FRESH air
• RECIRC air
• BI-LEVEL, FRESH AIR/RECIRC air (2-way flow)
5-12
TOYOTA Technical Training
Section 6
Automatic Temperature Control
Air Conditioning
Control Panel
Engine Coolant
Temp. Sensor
Room Temp.
Sensor
Evaporative
Temp. Sensor
Lock Sensor
Solar Sensor
ECM
Ambient
Temp. Sensor
A/C Magnetic
Clutch
Air Mix
Servo-motor
Air Mix Damper
Position Sensor
A/C Magnetic
Clutch Relay
Air
Conditioning
ECU
Air Outlet
Servo-motor
Air Outlet
Damper
Combination
Meter
Speed
Signal
Air Inlet
Servo-motor
Air Inlet
Damper
Position Sensor
A/C Pressure
Switch
Lesson
Objectives
Blower
Controller
Blower
Motor
1. Demonstrate the purpose of Automatic Temperature Control.
2. Identify and verify the function of various Automatic Temperature
Control components and sensors.
3. Verify thermistor operation and functions in the Automatic A/C Systems.
4. Verify the function of the Neural Network Control System.
5. Identify and diagnose a malfunctioning A/C sensor.
TOYOTA Air Conditioning and Climate Control – Course 752
Section 6
Automatic Temperature Control
Introduction
to Automatic
A/C
The heating, ventilation and air conditioning (HVAC) system in a house
contains a wall-mounted thermostat to control outlet temperatures,
distribution and fan speed. Changes are rarely made to the system other
than to reprogram the ON and OFF times and to switch the system ON
and OFF. In a vehicle, not all drivers wish to individually adjust all the
functions while driving. For this reason, Automatic A/C systems were
developed.
Automatic A/C
Temperature
Control
Automatic A/C is also referred to as “climate control.” Automatic A/C
systems function like conventional manual HVAC systems, but also offer
these functions:
• Ability to maintain a specific interior temperature selected by the
driver under a variety of temperature and solar conditions
• Automatic fan speed selection based on the heating or cooling need
• Automatic air distribution pattern based on the HVAC mode
• Automatic air intake control
In an Automatic A/C system, the refrigerant circuit, electronic controls
and safety systems are basically the same as a manual A/C system.
Toyota Automatic A/C systems add additional sensors and controls to the
basic system.
TOYOTA Air Conditioning and Climate Control – Course 752
6-1
Section 6
Here are some functions of the Automatic A/C controls on a late model
Toyota:
Outlet Air
Temperature
Control
Blower Control
Air Outlet
Control
In response to the temperature control setting, the outlet air temperature,
evaporator temperature sensor and engine coolant temperature sensor
compensations are used by the air mix control damper control to calculate a
target damper opening angle.
The temperature setting for driver and front passenger is controlled
independently in order to provide a separate air temperature for the right and
left sides.
This function controls the operation of the blower motor according to the
signals from the engine coolant temperature sensor, evaporator temperature
sensor and the solar sensor. In addition, it protects the blower motor
controller from the current surges when the blower motor is first activated.
When the AUTO switch is ON, automatic control causes the air mix control
servo-motor to rotate to a desired position for the correct outlet air temperature.
During operation, the potentiometer in the servo-motor detects the actual
damper opening so the system can match the actual opening to the desired
damper opening.
To prevent the front windshield from fogging up when the outside air
temperature is low, the system automatically switches the blower outlet to the
FOOT/DEF mode. Sensor inputs from engine coolant temperature, outside air
temperature, amount of sunlight, required blower outlet temperature and
vehicle speed.
Drives the servo-motor (for air inlet) according to the operation of the air inlet
control switch and fixes the dampers in the FRESH and RECIRC position.
Air Inlet Control
When selecting RECIRC mode under manual operation, if the outside air temp.
is low and refrigerant pressure has a malfunction, the A/C ECU automatically
switches the air inlet mode to the FRESH mode.
However, if the outside air temperature is much lower than the specified
temperature, in spite of the malfunction of the refrigerant pressure, the A/C
ECU automatically switches the air inlet mode to the FRESH mode.
When selecting RECIRC mode under manual operation, if the compressor
switches OFF, the A/C ECU automatically switches the air inlet mode to the
FRESH mode.
Compressor
Control
Seat Heater
Control
6-2
The control switches the magnetic clutch OFF when the blower motor is
switched OFF, when the engine coolant temperature is below a predetermined
value, an abnormal refrigerant pressure has been input or the discharge
temperature of the evaporator is below a predetermined value.
When the DEF mode switch is ON, the magnetic clutch relay activates
automatically to engage the compressor. In addition, when the blower is
switched OFF and the front defroster switch is switched ON, the blower will
activate in the automatic control condition.
The HI, LO and OFF settings of the seat heater can be switched by pressing
the seat heater switch (driver and front passenger). Based on signals from the
seat heater temperature sensor, the A/C ECU switches the seat heater relay
ON/OFF to regulate the set temperature. Switching the ignition to OFF
switches the seat heater OFF.
TOYOTA Technical Training
Automatic Temperature Control
Rear Window
Defogger Control
Outer Temperature
Indication Control
Self-Diagnosis
When the rear window defogger is ON, the rear window defogger and outside
rearview mirror heater operates. After 15 minutes, the system switches OFF.
Based on signals from the ambient temperature sensor, this control calculates
the outside temperature which is then corrected in the A/C ECU and
displayed in the A/C control panel.
Checks the sensor according to the operation of the A/C switches. The heater
control panel then displays a portion of the Diagnostic Trouble Code (DTC)
indicating a malfunction or a sensor check function.
Drives the actuators through a preset sequence according to the operation of
the A/C switches (actuator check function).
Automatic A/C
Components
An Automatic A/C system contains the following components:
Component
Function
A/C Electronic Control Unit (ECU)
Logic system to control system
components based on sensor inputs
Heater Relay (blower fan relay)
Confirms blower fan is ON
Temperature Sensors (thermistors):
Ambient Temperature Sensor
Temperature-sensitive resistors:
– Measures outside air
temperature
Humidity Sensor
Room Temperature Sensor
Evaporative Temperature Sensor
– Measures humidity level inside car
Engine Coolant Temperature
Sensor
– Measures engine coolant
temperature
Duct Sensor
– Measures dash outlet temperature
– Measures cabin air temperature
– Measures evaporator temperature
to prevent freezing
Pressure Switches (high and low)
Ensures system pressure is within
safe operation conditions
Belt Protection Sensor
Detects compressor speed
Solar Sensor
Detects sunlight for greater system
control
Engine RPM Sensor
Determines engine speed for idle
up mode
Speed Sensor
Determines vehicle speed
TOYOTA Air Conditioning and Climate Control – Course 752
6-3
Section 6
Customization
Features
Certain A/C modes can be “customized” or deselected using the
hand-held tester. For more information, refer to the diagnostics section
in the Vehicle Repair Manual.
Air Conditioner
DISPLAY (ITEM)
DEFAULT
CONTENTS
SETTING
SET TEMP SHIFT
(Air Inlet Mode)
NORMAL
To control with the shifted temperature
against the display temperature.
+2/+1C/NORMAL
–1C/–2C
AUTO
In case of turning the A/C ON when
you desire to make the compartment
cool down quickly, this is the function
to change the mode automatically to
RECIRCULATED mode.
MANUAL/AUTO
COMPRESSOR MODE
(Compressor Mode)
AUTO
Function to turn the A/C ON
automatically by pressing the AUTO
button when the blower is ON and
the A/C is OFF.
MANUAL/AUTO
COMPRS/DEF OPER
(Compressor/Air inlet
DEF operation)
LINK
Function to turn the A/C ON
automatically linking with the FRONT
DEF button when the A/C is OFF.
NORMAL/LINK
FOOT/DEF MODE
(Foot/DEF auto mode)
ON
Function to turn the air flow from
FOOT/DEF to ON automatically when
AUTO MODE is ON.
OFF/ON
AUTO BLOW UP
(Foot/DEF automatic
blow up function)
ON
Function to switch the blower level
automatically when the defroster is ON.
OFF/ON
FOOT AIR LEAK
(Foot air leak)
ON
Function to cut off the airstream felt
underfoot while the vehicle is moving.
OFF/ON
AMBIENT TMP SFT
(Ambient Temperature
Shift)
NORMAL
AIR INLET MODE
(Air Inlet Mode)
6-4
TOYOTA Technical Training
To control with the shifted ambient
temperature against the display
ambient temperature.
+3C/+2C/+1C
NORMAL/–1C/–2C/–3C
Automatic Temperature Control
A/C Amplifier
The ECU of a Toyota Automatic A/C system not only controls compressor
clutch and engine idle-up operation, it also controls outlet temperature,
airflow distribution and fan speed based on a determination of interior,
ambient temperature and humidity with a compensation for solar load.
MicrocomputerControlled
Auto A/C System
Auto A/C system
sensors and components.
Fig. 6-1
752f601
In addition, the A/C ECU monitors refrigerant pressure by controlling
the compressor clutch and provides signals to the ECM (engine control
module) for idle stabilization. In some vehicles, the compressor clutch
relay is not controlled directly by the A/C ECU but instead by the
powertrain control module that receives a signal from the A/C ECU.
TOYOTA Air Conditioning and Climate Control – Course 752
6-5
Section 6
The primary control unit for the compressor clutch circuit is the A/C
ECU. The ECU is a device that has an output current greater than the
input signals. The amplifier section of the ECU processes low current
signals from a number of sources to control a relay. The relay supplies
power to energize the compressor clutch. The relay also adds a further
level of amplification to the circuit since the power side of a relay can pass
more current than is needed to activate the control side.
The amplifier cycles the compressor clutch ON and OFF in order to provide
the most efficient transfer of heat at the evaporator while preventing the
evaporator from icing. The amplifier’s output signal also activates the
condenser fans at low speed and raises the engine idle speed (via the
engine and transmission ECU) to avoid stalling the engine whenever the
compressor switches ON.
Compressor
Clutch Circuit
Magnetic
Clutch Relay
Engine
and
Transmission
ECU
Main components:
• Prevents overcooling or
lock up.
• Prevents excessive
pressure.
Lock Sensor
A/C ECU
Compressor
Pressure
Switch
Fig. 6-2
752f602
Input Sensor Signals to the A/C Amplifier (A/C ECU)
Input Signal
Function
Temperature Selector
A/C Switch
Selects desired cabin (interior) temperature
Allows driver to switch compressor ON or OFF
Heater Relay (blower fan relay)
Confirms blower fan is ON
Thermistors:
Ambient Temperature Sensor
Room Temperature Sensor
Evaporative Temperature Sensor
Engine Coolant Temperature Sensor
Electrical temperature sensor:
– Measures outside air temperature
– Measures cabin air temperature
– Measures evaporator temperature to prevent freezing
– Measures engine coolant temperature
Pressure Switches (high and low)
Ensures system pressure is within safe operating condition
Belt Protection Sensor
Detects drive-belt speed
Solar Sensor
Detects sunlight for greater system control
Engine RPM Sensor
Determines engine speed for idle up mode
Speed Sensor
Humidity Sensor
Determines vehicle speed
Determines humidity of cabin air
6-6
TOYOTA Technical Training
Automatic Temperature Control
Automatic A/C
Control Panel
Compared to a manual system, an automatic A/C system features a
temperature control display marked with degrees and one or two
additional buttons on the control panel labeled AUTO to select automatic
fan speed and/or air distribution (almost like your home’s HVAC system).
When automatic A/C is desired, the driver selects the temperature in one
of three ways:
1. Slide lever
2. Rotating knob
3. Push button
Control Panels
1
Variable Resistor
Changes
Resistance in ECU
Variable Resistor
2
3
Changes
Resistance in ECU
Fig. 6-3
752f603
Each type of control causes a transistor circuit in the ECU to send a
variable voltage signal to the microprocessor. Changing the temperature
selector (or display) changes the signal value.
The primary input signal to the amplifier is a variable voltage from the
temperature selector that represents the desired interior temperature.
This potentiometer provides a variable resistance as it moves from cold to
hot (except at the extremes). In the chart on the following page, notice the
MAX COOL position (lower than 70° F) the resistance rises to infinity (∞Ω).
In the MAX HEAT position (over 85° F), the resistance goes to 0 ohms.
TOYOTA Air Conditioning and Climate Control – Course 752
6-7
Section 6
Temperature
Selector
Resistance Chart
Resistance, Ohms
3K
• Variable resistor.
• Higher temperature
setting has lower
resistance (Ω).
2K
1K
0
MAX
COOL
Temperature
Sensor Circuits
70°
77°
Set Temperature
85°
MAX
HEAT
Fig. 6-4
752f604
The objective of the Automatic A/C system is to reach an output
temperature based on a preset temperature. Toyota uses the terms “TSET”
to represent the preset temperature and “TAO” to represent the desired
output temperature. To be effective, the HVAC system must be able to
deal with variables such as the number of passengers in the vehicle,
relative outside temperature and the solar load in the vehicle. For
maximum comfort, the system anticipates conditions that will affect the
interior temperature before the temperature rises. Here are the various
inputs to the A/C ECU to determine TAO. It is only important to be aware
of the variables that determine TAO.
TAO (output temperature) = A x TSET – B x TR – C x TAM – D x TS + E
Temperature Variables
A
B
C
D
E
TSET
TR
TAM
TS
Servo-Motor
Control
6-8
Description
Set temperature coefficient
Room air temperature coefficient
Ambient air temperature coefficient
Solar radiation coefficient
Correct constant
Set temperature
In-car temperature
Ambient air temperature
Solar radiation
On current vehicles, servo-motors control the damper doors. A servo-motor
is an electric motor that contains a potentiometer (variable resistor) or a
multiple-position contact switch. This device acts like a position sensor to
provide feedback to the amplifier to confirm and to control the position of
the damper.
TOYOTA Technical Training
Automatic Temperature Control
The Automatic A/C system uses the air mix (“blend door”) system for
rapid and accurate temperature adjustment; the blend (air mix) door is
moved by the ECU-controlled servo-motor instead of a cable from the
temperature selector. Current water control valves are also operated by a
cable (via a servo-motor).
Distribution Control
(Servo-Motor
Controls)
DEF Position
FOOT Position
• Electrically controlled.
• Mover air mix or
blend doors.
BI-LEVEL Position
FACE Position
Fig. 6-5
752f605
Servo-Motor
Internal Circuit
Moving contacts provide
feedback on actual door
movement.
M
Fig. 6-6
Servo-Motor
752f606
Temperature sensor signals from various locations in the vehicle are
amplified inside the A/C ECU to produce a temperature value. This value
is then compared with the preset temperature (from the A/C control
panel) to determine the relative balance of the system. When all of the
amplified input signals meet the preset air temperature, the system is
said to be in balance; that is, the air mix servo-motor damper door
remains in position and the fan speed is kept low. Once the system is in
balance, there is no current flow to the air mix servo-motor.
TOYOTA Air Conditioning and Climate Control – Course 752
6-9
Section 6
When heat or solar load conditions create an imbalance, the ECU amplifies
the difference to operate one of two switching amplifiers according to
whether the interior must be warmer or cooler. The switching amplifiers
contain pairs of transistors and can conduct in either polarity to produce
a signal which controls the air mix servo.
Control of Blend
Air Damper
Since the servo-motor is an electric DC motor, changing the polarity
(+ and –) of the supply and ground causes the motor to rotate in different
directions, just like a power window motor. When there is a temperature
difference, one switching amplifier produces a positive voltage; the other
amplifier supplies a ground to move the air mix servo-motor in the
direction of cooler or warmer air delivery.
Depending on temperature requirements, the ECU selects a “target” damper
door position and measures the actual position with a potentiometer
(variable resistor) within the servo-motor. The ECU also monitors the
resulting change in temperature to verify the servo-motor(s) responds
appropriately.
Servo-Motor
Control Circuit
Switching amplifiers
control polarity to
air mix servo-motor.
+B
A/C ECU
Switching
Amplifier 1
M
Air Mix
Control
ServoMotor
Set Temperature
Servo-Motor
Feedback
In-Car Temperature
Switching
Amplifier 2
Ambient Temperature
Evaporator
Temperature
Solar Sensor
Fig. 6-7
752f607
6-10
TOYOTA Technical Training
Automatic Temperature Control
The A/C ECU will continue to output a control current to the servo until the
system is in “balance” as follows:
• Initially, this happens when the potentiometer in the servo-motor
indicates movement of the servo to a position which offsets the
temperature change.
• Later, the temperature in the vehicle will change to match the desired
temperature. Thus, the ECU will stop current flow to the servo-motor.
This system allows the temperature to “overshoot,” to rapidly adjust the
temperature in response to a temperature change. This is followed by
readjusting to the desired temperature setting.
Servo-Motor Circuit
Damper Door Linkage
(Moving Contacts)
Moving contacts
provide feedback on door
movement.
M
Limiter
ECU
Potentiometer
(Feedback)
COOL
WARM
Fig. 6-8
752f608
Pressure
Switches
Pressure switches can sense high or low pressures or both. These can be
separate switches or a single switch that senses multiple pressures (dual
or triple pressure switch). Pressure switches are normally closed and are
located in the high-pressure side of the system. When the switch opens
due to excessively high or low system pressure, the amplifier will disable
the compressor clutch to prevent component damage. For additional
information, refer to Multipressure Switch in Section 3.
TOYOTA Air Conditioning and Climate Control – Course 752
6-11
Section 6
Belt Protection
Sensor
To reduce the overall length of the engine, accessories may be driven by
just one or two belts. The A/C compressor and power steering pump are
usually driven by the same belt. However, if the compressor were to seize,
the belt could break which would cause a loss of power steering assist.
A belt protection system is used on all Toyota models to reduce the
potential safety hazard of a loss of power steering.
Lock Sensor
Belt Protection
Sensor
• Signals ECU that
compressor is locking.
Coil
• See text below.
Pulse Plate
O-Ring
Magnet
Front Shaft
Fig. 6-9
752f609
The belt protection circuit of the A/C amplifier or ECU monitors the
following signals:
• Engine rpm (Ne) is monitored at the Engine Control Module (ECM) or
at the ignitor.
• Compressor shaft rpm is measured by a magnetic pickup in the side of
the compressor housing.
The amplifier or A/C ECU will compare these signals to determine if Ne is
different from the compressor rpm by more than 60 percent for more
than 0.6 seconds. If it does, the system will:
• De-energize the compressor clutch relay. This will disengage the
compressor clutch.
• The amplifier will also cause the indicator lamp in the A/C button or
display to flash (to alert the driver of the malfunction).
• The system will reset when the ignition is switched OFF then ON again.
6-12
TOYOTA Technical Training
Automatic Temperature Control
Other conditions can cause the sensor to detect a difference in speed
between the engine and compressor:
• A system that is overcharged with refrigerant or refrigerant oil.
Compressor lockup is possible due to the extremely high pressures
that could result.
• A slipping A/C drive belt due to loose tension and/or oil or water on
the belt.
• A loss of signal to the amplifier from either the ignitor or the rpm
sensor.
• A malfunctioning compressor clutch due to an open circuit in the
source wire or in the clutch windings.
• Mechanical failure or lockup inside the compressor.
Thermistor
A thermistor is a temperature-sensitive resistor. Most electrical components
have a higher electrical resistance as the temperature increases. This is
called a positive temperature coefficient. Special thermistors with a
Negative Temperature Coefficient (NTC) provide accurate temperature
sensing for A/C and fuel injection systems. As the temperature increases,
the electrical resistance decreases. The A/C ECU reads the resultant
voltage to interpret the temperature.
Resistance vs.
Temperature of
Thermistor
• Resistance decreases
and temperature
increases.
7,000
Resistance (Ω)
• A/C temperature
sensors are thermistors.
8,000
6,000
5,000
4,000
3,000
2,000
1,000
0
0
(32)
5
(41)
20
30
15
35
10
25
40 °C
(50) (59) (68) (77) (86) (95) (104) (°F)
Temperature
Fig. 6-10
752f610
The A/C ECU supplies a fixed voltage to the sensor, then measures the
voltage drop across the thermistor. As the resistance changes, so does
the voltage drop. In this way, the amount of voltage drop created by the
thermistor is used by the amplifier as an input signal.
TOYOTA Air Conditioning and Climate Control – Course 752
6-13
Section 6
In-Car Sensor
(Thermistor)
The in-car sensor measures the air temperature inside the vehicle. In-car
sensors are usually located in the dash or center console. The actual
sensing element is very small, about 1/8″ (2 mm) diameter so it can
respond quickly to temperature changes.
To avoid being affected by solar radiation or hot car surfaces, it is shaded
from direct light but located in the air stream. Some models use an
aspirator powered by the air pressure in the blower case to draw interior
air past the sensor.
In-Car or Interior
Temperature
Sensor
Aspirator
• Thermistor
measures interior
air temperature.
Thermistor
Interior Air
Heater Unit
• Aspirator creates air
movement over sensor.
Fig. 6-11
752f611
Ambient
Temperature
Sensor
(Thermistor)
Outside temperature is measured by the ambient sensor so the system
can anticipate changes in cooling demand as the ambient temperature
changes. It is located in front of the radiator and condenser, but out of
the air stream.
Ambient
Temperature
Sensor
Ambient Temperature
Sensor
• Located at front grille.
• Senses outside
air temperature.
• Also controls
temperature gauge.
Fig. 6-12
752f612
6-14
TOYOTA Technical Training
Automatic Temperature Control
Solar Sensor
Sixty percent of the heat entering a vehicle comes from solar radiation.
Since the air in the car does not heat up immediately in bright sun, the
desired interior temperature can be maintained by anticipating the effect
of solar heat load. The solar sensor is usually located on top of the
instrument panel.
The solar sensor is a photo-diode rather than a thermistor. It normally
blocks the flow of current in both directions (it has a resistance of near ∞Ω)
except in the presence of light. When exposed to light, the photo-diode
biases the junction of the diode so that its resistance in one polarity falls
to near 0. It then gradually begins to conduct in one direction.
Solar Sensor
Solar Sensor
Filter
Portion
Sensor
Portion
Fig. 6-13
752f613
Like a temperature sensor, the solar sensor is supplied with a fixed voltage
so the A/C ECU can read the voltage drop to and sense the solar heat
entering the vehicle. The amplifier (or A/C ECU) can adjust the outlet air
temperature based on changes in sunlight before the interior temperature
changes. Some Toyota vehicles use a solar sensor that measures sunlight
falling from two angles to provide additional control over both driver and
passenger seating areas.
TOYOTA Air Conditioning and Climate Control – Course 752
6-15
Section 6
On current models, the A/C control unit controls blower speeds through
several steps according to various sensor inputs — the following chart
tracks blower air volume according to the amount of sunlight.
Stepless Fan
Speeds
HI
Sunlight on solar sensor
changes fan speed.
Blower
Air
Volume
LO
Large
Small
Amount of Sunlight
Sensor
(Thermistor)
Fig. 6-14
752f614
On some Toyota vehicles, air temperature in the air distribution ducts is
monitored by duct sensors. The A/C ECU changes the air distribution
dampers to adjust the airflow and air temperature accordingly.
Sensor Location
Thermistor sends
“air temperature”
signal to the
A/C control unit.
HV ECU
Solar Sensor
Room Temp. and
Humidity Sensor
A/C ECU
Fig. 6-15
752f615
6-16
TOYOTA Technical Training
Automatic Temperature Control
Maximum
Cool Damper
On vehicles with automatic temperature control, a MAX COOL Damper
Door can open (MAX COOL mode and FACE air-distribution modes) to
deliver additional cool air from the plenum to the dash vent outlets.
The damper is located after the evaporator. When energized, the damper
moves to allow cool air to bypass the heater core to deliver the lowest
possible air temperature to the outlet air vents.
Maximum
Cool Damper
Heater
Evaporator
Inlet
Adds flow on
MAX COOL.
Blower Motor
MAX COOL
Damper
FACE Vents
Fig. 6-16
752f616
Multimode
When the max cool damper is open, air resistance through the system
decreases. This allows more air to enter the vehicle through the system
without increasing fan speed or noise.
This feature blows air from all the vents during warm-up immediately
after the engine starts in cold weather. This prevents the windows from
fogging and helps to warm up the upper body.
TOYOTA Air Conditioning and Climate Control – Course 752
6-17
Section 6
Rear A/C Unit
Fig. 6-17
752f617
Rear
Air Conditioning
Some Toyota vehicles contain a separate rear air-conditioning system to
provide additional temperature control for rear passengers. The A/C
compressor supplies refrigerant to a separate A/C assembly mounted
behind the rear seat area.
The A/C compressor provides refrigerant for both the front and rear
systems. Some vehicles may or may not have a magnetic solenoid valve to
control refrigerant flow to the rear unit. If equipped, the magnetic valve is
part of the rear expansion valve.
6-18
TOYOTA Technical Training
Section 7
Automatic Temperature Control
Diagnosis and Repair
Display Diagnosis
00
All sensors are normal
11
Open or short circuit in room temperature sensor circuit
12
Open or short in ambient temperature sensor circuit
13
Open or short circuit in evaporator temperature sensor circuit
14
Open or short circuit in water temperature sensor circuit
21*
Open or short in solar sensor circuit
22*
Compressor lock detected
23*
Refrigerant pressure is either too high or too low
31
Abnormal air mix servo-motor potentiometer output voltage
32
Abnormal air servo-motor potentiometer output voltage
33
Abnormal air outlet servo-motor potentiometer output voltage
41
Abnormal air mix servo-motor operation
42
Abnormal air inlet servo-motor operation
43
Abnormal air outlet servo-motor operation
Lesson
Objectives
1. Perform various methods of testing an auto A/C system.
2. Retrieve auto A/C diagnostic codes from a vehicle.
3. Perform Sight, Sound and Touch Diagnostic Checks.
4. Perform various methods of testing auto A/C system components.
TOYOTA Air Conditioning and Climate Control – Course 752
Section 7
Automatic Temperature Control
Diagnosis and Repair
Diagnosis of
Automatic
A/C Systems
The most common automatic A/C system malfunctions tend to be the
result of basic air conditioning problems. These problems include:
• Refrigerant circuit, including leaks and inoperative components.
• Basic electrical malfunctions including open fuses, disconnected or
shorted wires and inoperative switches.
Just as with a conventional A/C system, a malfunctioning compressor
clutch can be caused by a number of reasons. In addition to the items
listed above, check the following circuits against published specifications:
• Evaporator thermistor
• Under-and-over pressure safety switches
• Connections to the ECU
• The wiring to and inside the clutch, and the coil ground
• The clutch control circuit of the amplifier
With such a range of input signals affecting system operation, it is often
easiest to test each circuit at the amplifier terminal. When the amplifier is
accessed, each circuit can be back-probed with voltmeter probes at the
main connector and quickly identified as “OK” or “NG” based on values in
service publications.
Diagnosis of an A/C complaint, even Auto A/C malfunctions, should
always begin with the “sight, sound and touch” checks of the refrigerant
system. Follow with a performance check using A/C pressure gauges to
determine charge level, operation of the compressor and other components.
• When the refrigerant system is fully operational and a mechanical
malfunction is present, the automatic A/C circuit itself could cause
variations between the desired temperature and the temperature at the
outlets.
• Excess resistance in the sensor circuits will result in colder-thandesired temperatures.
• Each servo-motor provides a signal to the amplifier to confirm its
position. If the internal potentiometer is inoperative, the system will be
unresponsive.
TOYOTA Air Conditioning and Climate Control – Course 752
7-1
Section 7
Diagnosis
Process
Toyota automatic A/C systems include circuits in the ECU to detect,
record and display codes for faults for various sensors, actuators and
circuits of the system. Operating some switches on the air-conditioning
control panel reveals any stored malfunction code. The self-diagnostic
codes remain stored, even when the ignition is switched OFF.
Self-Diagnosis
Functions
Turn Ignition Switch ON
With AUTO And
Switches Held Down
See Vehicle Repair
Manual by model for
specific procedures and
DTC numbers.
If Both AUTO And
Switch Are Not
Pressed At The Same Time
Indicator Check
OFF
OFF
Diagnostic
Code Check
(Sensor Check)
(Continuous Operation)
Diagnostic
Code Check
(Sensor Check)
(Stopped Operation)
AUTO
Actuator Check
(Continuous
Operation)
OFF
AUTO
Actuator Check
(Stopped
Operation)
OFF
OFF
Cancel Check Mode And Can
Start Air Conditioner Control
Fig. 7-1
752f701
A self-diagnosis system can perform the following functions:
• Compressor Lock – If the compressor shaft locks up during A/C
operation. The A/C switch indicator will blink.
• Indicator Check – Tests all indicator lights and buzzers of the
automatic A/C control panel four times (switch the ignition ON while
pressing and holding the AUTO and RECIRC switches).
• Diagnostic Code Check – Displays code numbers with the temperature
display of the automatic A/C control panel. A chart in the Vehicle
Repair Manual assigns a code number to a specific input (sensor) or
output (actuator) circuit. In addition, the chart refers to a page to
check the circuit.
Note the following details:
1. For current faults, the buzzer sounds when the code is displayed.
2. Past faults that have been stored in memory, but are not currently
present will display the code number without the buzzer.
3. Faults in the solar sensor or compressor lock sensor circuit are not
kept in memory after the ignition is switched OFF.
7-2
TOYOTA Technical Training
Automatic Temperature Control Diagnosis and Repair
A/C Sensor
Check Chart
Display Diagnosis
See Vehicle Repair
Manual for DTC numbers.
00
All sensors are normal
11
Open or short circuit in room temperature sensor circuit
12
Open or short in ambient temperature sensor circuit
13
Open or short circuit in evaporator temperature sensor circuit
14
Open or short circuit in water temperature sensor circuit
21*
Open or short in solar sensor circuit
22*
Compressor lock detected
23*
Refrigerant pressure is either too high or too low
31
Abnormal air mix servo-motor potentiometer output voltage
32
Abnormal air servo-motor potentiometer output voltage
33
Abnormal air outlet servo-motor potentiometer output voltage
41
Abnormal air mix servo-motor operation
42
Abnormal air inlet servo-motor operation
Abnormal air outlet servo-motor operation
43
Fig. 7-2
• Actuator Check – Test Recirc Control. Press the REC switch to begin
the test sequence for actuators. This process causes the system to
engage eight or 10 different combinations of fan speed, distribution,
temperature and intake modes in a preset sequence. The steps can be
advanced manually by repeatedly pressing the UP (▲) switch. The
Vehicle Repair Manual includes a chart showing the conditions for each
of the steps.
A/C Actuator Test
Function Chart
• See Vehicle Repair
Manual by model for
specific conditions.
Conditions
Step Display
No.
Code
Blower
Speed
1
0
OFF
2
1
1
3
2
4
3
5
4
6
5
7
6
8
7
Airflow Vent
Face
Air Inlet
Fresh
Air Mix
Damper
Position
Cool Side
(0% open)
OFF
OFF
Fresh/Recirc.*
Recirc.
3
Magnetic Water Valve
Clutch
VSV**
Bi-level
Fresh
ON
Cool/Hot
(50% open)
ON
Foot II
4
Foot I
Hot side
(100% open)
Foot/Def.
5
Def
*Indicator light for “fresh (
)” mode goes on.
**Servo-motor controlled, some vehicles.
Fig. 7-3
752f703
TOYOTA Air Conditioning and Climate Control – Course 752
7-3
Section 7
Testing Sensor
Inputs
To review, the in-car ambient, coolant and evaporator temperature sensors
are all Negative Temperature Coefficient (NTC) thermistors, so their
resistance rises as the temperature decreases.
Test procedures and specifications for each circuit are in the Vehicle
Repair Manual. Many automatic A/C sensors are tested while unplugged
using an ohmmeter. Some circuits can be tested at the connector nearest
the sensor. In other cases, you can remove the A/C control panel to access
the multipin connectors on the back of the panel.
The test values for thermistors are described in a chart or a graph that
shows the resistance values at different temperatures. As a rule of
thumb, almost all NTC thermistors have a room temperature value of
1,500 – 2,000 ohms (1.5K – 2K1). Compare the conditions and the ohmmeter
display with the table or graph.
Thermistor Test
With Ohmmeter
Resistance increases
as temperature
decreases.
Fig. 7-4
752f704
This system contains a “fail-safe” mode that allows it to operate even
when a primary sensor circuit has malfunctioned. In the following
illustration, consider how the system might respond to an open circuit in
one of the temperature sensor circuits:
• An open circuit has a resistance of infinite ohms ('1).
• Very high resistance from an NTC might indicate an extremely cold
temperature. The system might be expected to respond by producing
maximum heat until the interior temperature equals the preset
temperature. However, this countermeasure will never happen.
To avoid this, the A/C ECU may substitute a fixed value for an
out-of-range sensor circuit. This would allow the system to continue
operation with reduced responsiveness.
7-4
TOYOTA Technical Training
Automatic Temperature Control Diagnosis and Repair
Open in
Auto A/C Sensor
Circuit
ECM defaults to fixed
value in open circuit.
A/C
ECU
In-Car
Sensor
Open
Circuit
Fig. 7-5
Solar Sensor
Testing the
Solar Sensor
752f705
Alternately cover, then illuminate the sensor while the system is in the
AUTO mode. When illuminated (not covered), the fan speed should
increase noticeably and the outlet temperature should decrease slightly.
With a multimeter, test the solar sensor with a bright light. This decreases
its resistance and increases the voltage when checked at the harness
connector.
Solar Sensor Test
With Ohmmeter
Electric Light Bulb
(Not Fluorescent)
• Some solar sensors
are dual action
(driver/passenger).
• Two DTC (21/24)
numbers for dual type.
Fig. 7-6
752f706
TOYOTA Air Conditioning and Climate Control – Course 752
7-5
Section 7
Testing
Servo-Motors
During a diagnostic test of system actuators, one or more operational
modes may not respond correctly. The diagnostic test will direct you to
test specific actuators. The test will be one of two types: Functional and
Circuit.
A Functional Test consists of applying battery voltage across the motor
terminals of the servo-motor harness connector. The arm motion should
be smooth to the end of its travel. With reverse polarity, the arm should
move smoothly in the opposite direction.
Servo-Motor Test
Cool
20
• Position changes with
power applied and
change of polarity.
2
6
70
2
6
Hot
Fig. 7-7
752f707
A potentiometer is built into some servo-motors so the ECU can determine
the arm position of each one. These circuits are important for proper
system operation. The variable resistor can be measured with an ohmmeter
as the servo-motor is energized during the Functional Test described
above.
Servo-Motor Test
• Feedback signal
to ECU that door
has moved.
• Pin locations vary
by model.
Fig. 7-8
752f708
7-6
TOYOTA Technical Training
Automatic Temperature Control Diagnosis and Repair
Automatic
A/C System
Repair
Techniques
Due to similarities between the refrigerant and control systems among
different automatic A/C systems, most complaints can be diagnosed
using standard A/C system tools and techniques. Take all appropriate
measures in regard to personal safety around pressurized gases and
electrical devices. Observe standard procedures for refrigerant recovery,
recycling, evacuation and charging.
Automatic A/C systems may require wiring harness repairs, particularly
following a collision. Since these systems sense temperature conditions
by looking at electrical resistance, proper wiring repairs are very important
to system operation. Be sure to use the components and procedures of
the Toyota Wiring Harness Repair Kit to avoid adding excess resistance to
the automatic A/C circuit.
A/C System
Odors
A/C system odors are a common complaint among users, especially after
start-up. Odors are primarily caused by one of two things:
1. Dirt or microscopic particles which are trapped in the evaporator, then
later blown into the vents. This results in a “musty” or “stale” odor.
2. Microbes growing on the evaporator surfaces. These are later blown
into the vent ducts. Microbes are small living bacteria which are carried
into the evaporator case, then grow in the warm, moist environment.
The Xenon tube in some rear A/C systems helps reduce these microbes.
3. Change the clean air filter when odor is detected.
There is no permanent mechanical repair for either type of odor. Replacing
the evaporator or cleaning it with a strong chemical is only a temporary
fix. The driver must change how the system is used.
To avoid evaporator odor, operate the system in the FRESH mode rather
than in RECIRC. This allows a flow of clean, fresh air over the evaporator.
The compressor should be switched OFF with the A/C switch while the
fan runs for several minutes before shutting off the engine. In addition,
park the vehicle with the windows slightly open with the system in the
FRESH mode to allow the evaporator to dry out.
TOYOTA Air Conditioning and Climate Control – Course 752
7-7
Section 7
Clean Air Filter
Spreading
Type
Activated
Charcoal
• Located behind
Glove Box.
Exhaust
Gas Smell
Clean Air
Clean Air Filter
Deodorizing Layer
Fig. 7-9
752f709
Late model Toyota vehicles have a replaceable fabric air filter that prevents
microbes and dust from entering the system and settling on the evaporator.
Positioned upstream (in front) of the evaporator, the filter fibers have a
static charge to attract small particles to the filter surface.
If air volume is low, the air filter could be clogged. Replace the filter.
Do not attempt to clean it.
7-8
TOYOTA Technical Training
Automatic Temperature Control Diagnosis and Repair
Diagnosing the
Automatic A/C
System
The A/C ECU has a self-diagnosis feature that stores operation failures
in memory. DTCs can be displayed by operating switches on the A/C
control panel. DTCs remain in memory even when the ignition is OFF.
As described in Section 8, a Fuzzy Logic system in some vehicles
attempts to simulate human control of the HVAC system using input
sensors, a sophisticated A/C ECU and output actuators. Vehicles with
such systems also contain a self-diagnosis feature.
Function
Description
Indicator Check
Checks indicator lights and temperature setting
display.
Sensor Check
Checks the past and present malfunctions of the
sensors and clears past malfunction data.
Actuator Check
Checks against actuator check pattern to make sure
if blower motor, servo-motors and magnetic clutch
are operating correctly according to signals from the
ECU. Checks sequence of modes and fan speeds to
check airflow from each outlet. Compare with air
outlet and airflow chart.
TOYOTA Air Conditioning and Climate Control – Course 752
7-9
Section 7
Notes
7-10
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 7-1 (IN-CLASS)
ATC Sensors and Controls
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
Given this worksheet, a Vehicle Repair Manual, and a vehicle you will identify the various A/C sensors used in
Toyota vehicles and successfully diagnose a sensor malfunction.
Background:
Vehicles with ATC use several sensors to sample the air temperature or airflow in and out of the vehicle.
Knowing where these sensors are located and how they look will help you work more efficiently in diagnosing
and repairing the system. There are three possible malfunctions that occur with sensor-driven control systems.
•
Sensor malfunction
•
Control unit malfunction
•
Problem in sensor circuit (harness, connector, etc.)
Tools and Equipment:
•
Vehicle Repair Manual (TIS)
Section 1
Sensor Types
Description
Solar Sensor
A photo diode component that sends voltage signals to the A/C ECU
based on sun load.
Compressor Lock Sensor
A reed switch that sends voltage pulses to the A/C ECU indicating
rotation of the compressor, pulses are measured against engine speed
to determine if the compressor is rotating.
Room Temperature Sensor
A sensor using a thermistor to indicate changes in the cabin
temperature.
Ambient Temperature Sensor
A sensor used to sense the ambient air outside the vehicle using a
thermistor.
Evaporator Temperature Sensor
Uses a thermistor to signal the A/C control unit when temperature
changes occur in the evaporator.
Engine Temperature Sensor
This signal comes from the ECU and indicates engine temperature
during warm-up control.
TOYOTA Technical Training
7W1-1
Worksheet 7-1
Use the Vehicle Repair Manual to evaluate the condition of various sensors. Always refer to the appropriate
Vehicle Repair Manual as sensor values change from year to year.
Note: If a sensor is not available on your test vehicle, mark the answer area with “NA,” then proceed to the next
question.
1. Locate the section in the Vehicle Repair Manual that describes the diagnostics for the A/C system for the
test vehicle. What page describes various DTCs for the A/C system?
____________________________________________________________________________
2. Locate and record the trouble code for the Compressor Lock Sensor. _____________________
3. What happens when the ECU records a compressor lock sensor DTC (22)?
_______________________________________________________________
4. Locate and identify the Compressor Lock Sensor on your vehicle, then use a Digital Multi-Meter (DMM) to
determine if the sensor is good.
Sensor reading: _______________________
Good _____________ NG _______________
5. What does the Vehicle Repair Manual suggest if the sensor tests okay but a DTC appears for this problem?
_______________________________________________________________
6. Locate the section in the Vehicle Repair Manual to inspect the Room Temperature Sensor Circuit.
7. What pages in the Vehicle Repair Manual describe this inspection?
___________________________________________
8. What type of equipment is suggested in the Vehicle Repair Manual to heat the Room Temperature Sensor in
order to inspect the sensor?
________________________________________________
9. List the resistance specifications (low and high) for the Room Temperature Sensor.
Low ____________________________ High ______________________________
10. What happens to circuit resistance when the sensor is exposed to more heat?
_________________________________________________________________________________________
11. What is the DTC number for the Evaporator Temperature Sensor Circuit? _______________________
7W1-2
TOYOTA Technical Training
ATC SENSORS AND CONTROLS
12. Place the evaporator temperature sensor in 60ºF water. What is the resistance reading?
__________________________________________________________________________________________
13. What type of signal is sent to the control unit when the evaporator temperature sensor is operating?
______________________________________
14. List the two A/C control assembly terminals to check the Evaporator Temperature Sensor.
__________________________________________________________________________________________
Summary:
Check DTCs first when you suspect a sensor is not providing the correct input to the system.
Note: It is also important to verify that there is actually a malfunction in the system. Customers will often expect
something from an Automatic A/C system which it cannot deliver. These complaints are often about
airflow, time to cool down or heat, window fogging, or the difference between what they think the system
should do versus what it is designed to do.
The bottom line is that you must obtain as much information from the customer as possible. Knowing the
exact customer complaint can save you time and money in the long run.
Instructor Sign Off: ______________________________________
TOYOTA Technical Training
7W1-3
Worksheet 7-1
Notes
7W1-4
TOYOTA Technical Training
ATC SENSORS AND CONTROLS
ATC Sensors and Controls
Name: _____________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 7-1 using the ATC Sensors and Controls worksheet in the shop. Ask the instructor if you
have any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
Purpose of each sensor
Location of each sensor
Purpose of compressor lock sensor
Thermistor changes with temperature
Locating sensor specifications
Testing sensors
TOYOTA Technical Training
7W1-5
Worksheet 7-1
Notes
7W1-6
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 7-2 (ON-CAR)
Automatic Air Conditioning “Self-Diagnosis” Testing
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
Given this worksheet and a Vehicle Repair Manual, you will correctly perform a “self-diagnosis” to retrieve
A/C-related Diagnostic Trouble Codes (DTCs) and check the operation of all servo-motors, actuators and
sensors of a Toyota Automatic Air Conditioning System.
Background:
Besides receiving inputs from system sensors and controlling actuators, the A/C ECU also displays and stores
DTCs in its memory in order to easily diagnose malfunctions in the system. This exercise will give you practice in
displaying and retrieving DTCs.
Tools and Equipment:
•
Vehicle Repair Manual (TIS)
•
Vehicle with Auto A/C
Retrieve Diagnostic Trouble Codes (DTCs)
1. Use the appropriate Vehicle Repair Manual as a guide in performing A/C self-diagnosis.
Vehicle Repair Manual: ______________________ Page number: __________
2. In the Vehicle Repair Manual, what are three checks available on this system under the category, “LIST OF
OPERATION METHODS?”
____________________________________
____________________________________
____________________________________
3. Where are DTCs displayed during the manual DTC Check mode?
____________________________________________________________________________
4. What two switches are depressed at the same time to access the Indicator Check mode?
_________________________ and ___________________________
5. Identify the events that happen in order when entering the Indicator Check mode?
a. ______________________________________________________
b. ______________________________________________________
TOYOTA Technical Training
7W2-1
Worksheet 7-2
6. What DTCs are in memory?
_________________________________________________________
_________________________________________________________
7. Disconnect the A/C pressure switch connector. What DTC appears? ______________________________
8. What are “hard” codes?
_________________________________________________________________________________________________
9. How are hard codes erased? _____________________________________________________
Note: Some DTC sensor codes self-clear when the malfunction is corrected.
10. Reconnect the pressure switch connector. What happens? ____________________________________________
Actuator Test
11. What is the procedure to perform an actuator test?
a.
__________________________________________________________
b. __________________________________________________________
12. What page in the Vehicle Repair Manual identifies the air volume and air register when selecting various air
distribution modes? ___________________________________________
13. What do the different size circles indicate in an air distribution chart?
_____________________________________________________________
7W2-2
TOYOTA Technical Training
AUTOMATIC A/C “SELF DIAGNOSIS” TESTING
14. What switch do you press to check each register outlet for fan speed and airflow volume?
______________________________________________________________.
15. Ignition OFF.
16. Recheck for stored DTCs. Clear if necessary.
17. Return the station back to its original condition.
Instructor Sign Off: ______________________________________
TOYOTA Technical Training
7W2-3
Worksheet 7-2
Notes
7W2-4
TOYOTA Technical Training
AUTOMATIC A/C “SELF DIAGNOSIS” TESTING
Automatic Air Conditioning “Self-Diagnosis” Testing
Name: ___________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 7-2 using the Automatic A/C “Self Diagnosis” Testing worksheet in the shop. Ask the
instructor if you have any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
Locating the code retrieval procedure
How to obtain stored DTC in memory
Determine what DTC indicates
Checking solar sensor
Perform actuator test
Checking airflow from outlets
TOYOTA Technical Training
7W2-5
Worksheet 7-2
Notes
7W2-6
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 7-3 (ON-CAR)
C-Best Settings Using the Hand-Held Tester
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
Given this worksheet, a Toyota vehicle and the Toyota Hand-Held Tester, you will access the Auto A/C menus
and record component details.
Background:
The C-Best Hand-Held Tester provides access into the electronic circuitry of many vehicle systems. Your skill in
using this device will help you identify and diagnose A/C-related malfunctions.
Tools and Equipment:
•
Toyota Hand-Held Tester
•
Prius Vehicle
•
Prius Repair Manual
Retrieve A/C Data
1. Ignition OFF.
2. Connect the tester to the DLC3 connector on the vehicle.
3. Ignition ON.
4. Select “DIAGNOSIS” from the “APPLICATION
SELECT” menu.
5. Select “OBD/MOBD.”
6. Select “Vehicle.”
APPLICATION SELECT
1: DIAGNOSIS
2: CUSTOMIZE
3: ECU REPROGRAM
7. Select “Air Conditioner” from the “OBD/MOBD”
menu.
8. Verify DLC3 Connection.
9. From the diagnostic menu, select “DATA LIST.”
DIAGNOSTIC MENU
AIRCON
10. Select “All” from the “SELECT DATA” menu.
11. From the DATA LIST, what is the position of the Air
Inlet Damper Door (“A/I Damp Pos”)?
1:
2:
3:
4:
DATA LIST
DTC INFO
ACTIVE TEST
SNAPSHOT
___________________________________
TOYOTA Technical Training
7W3-1
Worksheet 7-3
12. Press the “Recirc _ Auto _ Fresh” buttons on the A/C control panel in turn, then record the damper door
opening percentages from the DATA LIST in each of these modes:
a.
Recirc ______________________
b. Auto
______________________
c.
______________________
Fresh
Note: In AUTO mode, the Auto A/C system selects RECIRC or FRESH depending on the set temperature
and cooling requirements.
13. What do the letters “D” and “P” on the DATA LIST mean?
_________________________________________________________________________
14. “Ambient temperature” is the temperature _________________________________ the vehicle.
15. Engine ON.
Note: You may have to reset the tester to read the DATA LIST.
16. Place the A/C system in “AUTO,” set the interior temperature to 70º F, wait 60 seconds, then record the
temperature of the following items from the DATA LIST:
Item
DATA LIST item
Duct temperature -D
DUCT TEMP-D
Duct temperature -P
DUCT TEMP-P
Evaporator temperature
EVAP TEMP
Room (interior) temperature
ROOM TEMP
Ambient temperature
AMBI TEMP
Temperature
_________________ ºF
_________________ ºF
_________________ ºF
_________________ ºF
_________________ ºF
17. Solar Sensor:
a.
What does the solar sensor measure? __________________________________________________________
b. What is the current status of the solar sensor? ___________________________________________________
7W3-2
TOYOTA Technical Training
C-BEST SETTINGS USING THE HAND-HELD TESTER
c.
If the vehicle is in artificial light, shine an incandescent light source (flashlight) at the sensor, then record
the results:
_____________________
d. If the vehicle is in direct sunlight, place a shield over the sensor, then record the results:
_____________________
18. Select Customize menu and Air Conditioning __________________________
19. List three A/C functions that can be customized with the Hand-held Tester
_________________________________________
_________________________________________
_________________________________________
20. What is “Temp shift” and “Sensitivity” options? ______________________________________________________
21. Engine OFF, Ignition OFF.
22. Switch the Hand-Held Tester OFF, then remove from the vehicle.
23. Return the work station to the same condition as you found it.
Instructor Sign Off: ______________________________________
TOYOTA Technical Training
7W3-3
Worksheet 7-3
Notes
7W3-4
TOYOTA Technical Training
C-BEST SETTINGS USING THE HAND-HELD TESTER
C-Best Settings Using the Hand-Held Tester
Name: ___________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 7-3 using the C-Best Settings Using the Hand-Held Tester worksheet in the shop.
Ask the instructor if you have any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
Connect the hand-held tester
Select C-Best menu
Select “customizing” feature
Select DATA LIST
TOYOTA Technical Training
7W3-5
Worksheet 7-3
Notes
7W3-6
TOYOTA Technical Training
Section 8
Air Conditioning: Hybrid Vehicles
Lesson
Objectives
1. Identify unique A/C System Components and their function in a
hybrid vehicle.
2. Identify safety and service procedures unique to hybrid vehicles.
3. Identify unique diagnostic procedures when troubleshooting hybrid
A/C malfunctions.
TOYOTA Air Conditioning and Climate Control – Course 752
8-1
Section 8
Air Conditioning: Hybrid Vehicles
Hybrid vehicles (internal combustion engine with electric motor and
battery pack) have unique issues to meet the heating, ventilation and
air conditioning requirements during vehicle operation. For example,
since the electric motor provides primary power during certain operating
conditions, normal belt or direct drive mechanisms must continue to
operate even though engine power is OFF. This section describes the
HVAC system, components and unique diagnostic issues inherent with
current hybrid vehicles.
A/C
Components
The basic principles of air conditioning apply to both existing gasolinepowered vehicles and hybrid electric-gasoline-powered vehicles. The basic
air conditioning components discussed in the previous chapters also apply
to hybrid vehicles. However, in a hybrid A/C system, all components are
optimized for peak efficiency with low power consumption. In some cases,
certain components are designed to operate in both mixed-power modes:
Hybrid A/C
Components
Typical component
locations.
Inverter
• A/C Inverter
Condenser
A/C Water Pump
Gateway ECU
Ambient Temp. Sensor
Steering Pad Switch
ECM
Electric Inverter
Compressor
HV ECM
Combination Meter
• Meter ECU
Solar Sensor
Room Temp. and
Humidity Sensor
A/C ECU
Fig. 8-1
752f801
TOYOTA Air Conditioning and Climate Control – Course 752
8-1
Section 8
A/C Component
Comparison
Component
Typical A/C system
Hybrid A/C system
Expansion valve
same
A/C compressor
Belt-driven scroll-type Electric-powered scroll-type
Evaporator
Condenser
Receiver-drier
same
Refrigerant lines
Refrigerant
Refrigerant oil
Warning:
ND8/9
ND11
Hybrid electrical vehicles use high voltage systems (orange color wiring)
which can result in serious injury or death if insulated gloves are not
worn and safety procedures are not used. It is extremely important to
refer to the appropriate sections of the Repair Manual prior to working
on any high voltage systems including the air conditioning compressor.
Technicians should attend the Hybrid training classes (071, 072) prior to
working on hybrid model high voltage systems or components.
Safety Procedures
Repairs performed incorrectly on the Hybrid Control System could
cause electrical shock, battery leakage or explosion. Be sure to follow the
procedures below:
• Shut off the vehicle. If vehicle has smart key system, disable it and
make sure the key fob is 15 feet away from vehicle.
• Disconnect the negative (–) terminal cable from the 12V auxiliary battery.
• Wear insulated gloves.
• Remove the Service Plug and do not make any repairs for FIVE minutes.
• Before touching a high voltage cable (orange) or any cable you cannot
identify, use a voltage tester to confirm that the voltage through the
cable is 12V or less.
• After removing a high voltage cable, be sure to cover the terminal end
with rubber or vinyl tape.
• Use insulated tools, when available.
• Do not leave tools or parts (nuts, bolts, etc.) inside the cabin.
• Do not wear metal objects (risk of short circuit).
8-2
TOYOTA Technical Training
Air Conditioning: Hybrid Vehicles
A/C
Compressor
In order to reduce internal vehicle temperatures in a hybrid vehicle, the
A/C compressor, being the driving force that circulates refrigerant, must
operate even when the engine is OFF. Current hybrid vehicles use an
Electric Inverter Compressor. Instead of belt-driven, the compressor is
driven by an electric motor built into the compressor housing and
powered by alternating current (AC voltage) from the vehicle’s power
supply system. Except for the portion that is actuated by the electric
motor, the basic construction and operation of this compressor are the
same as the scroll compressors used in other Toyota vehicles.
Electric Scroll-type
A/C Compressor
Suction Hose
Electric motor drives
scroll portion.
Fig. 8-2
Discharge Hose
752f802
The alternating current that drives the compressor motor is supplied by
an A/C inverter that is integrated in the hybrid system inverter. An
inverter is an electronic device that changes DC to AC volts (or vice-versa).
As a result, during vehicle operation, the air-conditioning control system
can operate without depending on the gasoline engine to drive it. Thus,
the hybrid vehicle provides a continuous-running A/C system that
operates with low fuel consumption.
Since the compressor is energized by electricity, an ECU can control its
speed. By controlling the speed in this manner, cooling and dehumidification
performance and power consumption are optimized.
Similar to scroll compressors used in other Toyota vehicles, the Electric
Inverter Compressor also contains a built-in oil separator. Because the
scroll sections are sensitive to excess refrigerant oil in this area, the oil
separator helps separate the compressor oil from the refrigerant gas that
enters the compressor.
TOYOTA Air Conditioning and Climate Control – Course 752
8-3
Section 8
Fixed Scroll
A/C Compressor
Oil Separator
Helps separate
excess oil before
entering compressor.
Variable Scroll
Separator
Motor Shaft
Discharge Port
Refrigerant Oil
Brushless Motor
Fig. 8-3
752f803
Current hybrid systems use a refrigerant oil with the designation ND11.
This oil ensures the proper electrical insulation qualities needed due to the
high voltage used to drive the electric motor (approx. 200 VAC). Currently,
Toyota specifies using only ND11 refrigerant oil in hybrid A/C compressors.
Other
Hybrid HVAC
Components
Heater Core
Typically, water-cooled engines cannot produce heated interior air until
the coolant warms up and transfers heat through the heater core. In a
hybrid vehicle, this is more problematic due to the gasoline engine
cycling ON and OFF resulting in longer warm-up periods. The engine
coolant heater core itself is a compact, lightweight and highly efficient
straight-flow unit to ensure maximum heat transfer.
To help create warm air in the vehicle interior during these periods, Toyota
hybrid vehicles incorporate a Positive Temperature Coefficient (PTC)
heating element in the heater core. A PTC element produces heat when
electric current passes through it. The vehicle A/C ECU controls when
current is applied to the PTC element. The air circulating through the
heater core fins is thus quickly brought up to temperature to warm the
vehicle interior.
8-4
TOYOTA Technical Training
Air Conditioning: Hybrid Vehicles
PTC Heating
Element
Fin
Provides warm air
as needed.
Electrodes
PTC Element
Insulation Film
Warm Water
Core Tube
Cool Air
Warm Air
Fig. 8-4
PTC Heater
Warm Water
752f804
Some vehicles have an additional PTC heater installed in an air duct of
the blower housing. This additional PTC heater helps increase the air
temperature in the ducting.
PTC Heater in
Blower Housing
Adds additional
heating capacity.
Fig. 8-5
PTC Heater
TOYOTA Air Conditioning and Climate Control – Course 752
752f805
8-5
Section 8
Water Pump
The hybrid electric water pump provides continuous coolant flow through
the heater core even if the engine shuts OFF during normal vehicle
operation. This takes advantage of any heated coolant in the system and
increases heater core performance.
Electric
Water Pump
to Heater
Supplies engine coolant
to heater as necessary.
from Engine
Fig. 8-6
752f806
Temperature
Control System
In a conventional automatic air-conditioning control system, the A/C ECU
calculates the required outlet air temperature (TAO: Temperature Air
Outlet) for the preset temperature. These preset calculations are based on
temperature information from various sensors in the vehicle. Auto A/C
systems maintain a stable interior temperature by automatically controlling
servo-motors and blower motor speeds in order to arrive at the calculated
TAO. However, typical Automatic A/C systems provide little control.
In some vehicles, a Fuzzy Logic system attempts to simulate human
control of the HVAC system using input sensors, a sophisticated A/C ECU
and output actuators. Vehicles with such systems also contain a
self-diagnosis feature.
8-6
TOYOTA Technical Training
Air Conditioning: Hybrid Vehicles
A/C ECU
Communication
Combination Meter
System function and
A/C display information.
A/C
AUTO
Meter ECU
A/C ECU
BEAN
Gateway ECU
AVC-LAN
OUTSIDE
TEMP
CLIMATE
66
Air-Conditioner
DISPLA
LO
HI
AUDIO
INFO
FRONT
A /C
AUTO
75
TEMP
A/C
REAR
OFF
TEMP
AUTO
Multi-Display
TEMP
Fig. 8-7
Steering Pad Switch
752f807
The A/C ECU calculates the target evaporator temperature that is based
on the vehicle interior humidity level and the windshield glass inner
surface humidity (calculated from data sent by the humidity sensor, solar
sensor, room temperature sensor, mode damper position and the status
of the windshield wiper). The ECU then automatically determines the
ideal combination of outlet air temperature, air volume, airflow direction
and compressor speed for optimal passenger comfort.
TOYOTA Air Conditioning and Climate Control – Course 752
8-7
Section 8
Typical Hybrid A/C
System Diagram
A/C system optimized
for best comfort, good
fuel economy.
Air Mix
Servo-Motor
Fan Relays
Air Mix
Damper
Position Sensor
Heater Relay
Air Outlet
Servo-Motor
Air Outlet
Damper
Position Sensor
Air Inlet
Servo-Motor
Air Inlet
Damper
Position Sensor
A/C ECU
Room Temp.
Sensor
Blower Pulse
Controller
Blower Motor
Rear Defogger
Relay
Rear Defogger
Mirror Heaters
Relay
Mirror Heaters
PTC Relay
PTC Heater
(in Heater Core)
PTC Relay
PTC Heater
(in Air Duct)
Meter ECU
A/C
Indicator Light
BEAN
Humidity
Sensor
AVC-LAN
Multi-Display
Gateway ECU
Evaporator
Temp. Sensor
ECM
• Engine Coolant Temperature
• Ambient Temperature
• Engine Speed
Solar Sensor
Battery ECU
• Room Temp. and Ambient Temp.
Sensor signal Reception
• Blower Motor Mode Reception
• HV Batter Cooling Signal Reception
Wiper Switch
Converter
CAN
Steering Pad
Switch
HV ECU
• Compressor Control Signal Reception
• Blower Motor Mode Reception
• Water Pump Control Signal Reception
A/C Inverter
Water Pump
Relay
Electric Inverter
Compressor
A/C Water Pump
Fig. 8-8
Pressure
Switch
752f808
8-8
TOYOTA Technical Training
Air Conditioning: Hybrid Vehicles
Electric Inverter
A/C Compressor
Control
To arrive at the best comfort levels and to produce the best fuel economy,
the A/C ECU calculates the target A/C compressor motor speed based on
the target evaporator temperature and the actual evaporator temperature
(detected by the evaporator temperature sensor). The A/C ECU then
transmits the target speed to the hybrid vehicle’s High Voltage (HV) ECU.
The HV ECU controls the A/C inverter based on the target speed data to
rotate the compressor at the ideal speed.
Compressor
Speed Control
Electric Inverter
Compressor
Fuzzy Logic calculates
sensor data in A/C ECU.
A/C Inverter
Inverter
Control
A/C ECU
Room Temp.
Sensor
Humidity
Sensor
Target
Compressor
Speed
Calculates the
target
compressor
speed in
accordance with
various input
conditons
HV ECU
Solar Sensor
Evaporator
Temp. Sensor
Ambient Temp.
ECM
Air Outlet
Damper
Position Sentor
Wiper Switch
Wiper Motor
Ambient Temp.
Sensor
Fig. 8-9
752f809
TOYOTA Air Conditioning and Climate Control – Course 752
8-9
Section 8
Room
Temperature and
Humidity Sensor
The latest hybrid HVAC systems use a humidity sensor function combined
with the room temperature sensor. Detecting humidity in the vehicle
interior optimizes the amount of dehumidification during A/C operation.
This results in the A/C compressor consuming less power and creates an
ideal humidity level inside the vehicle.
A resistance film inside the sensor absorbs and releases air in the interior.
During the absorption and release process, the humidity-sensing film
expands (during humidity absorption) and contracts (during drying). As the
resistance film expands and contracts, the clearance between the carbon
particles in the resistance film changes which increases or decreases its
electrical resistance. The A/C ECU then determines the amount of
humidity by measuring the resistance between the electrodes.
Humidity-sensing Resistance Film
Humidity Sensor
Combined with
temperature sensor to
regulate interior
humidity levels.
High
Electrodes
Output
Voltage
A/C
ECU
Low
Low
High
Relative
Blower Pulse
Controller
Room Temp.
Sensor
Fig. 8-10
752f810
The blower pulse controller controls the voltage that is supplied to the
blower motor according to the duty cycle signals input by the A/C ECU.
This arrangement generates a smaller amount of heat in the blower
controller compared with earlier versions. Thus, there is less power loss
and increased fuel economy.
Blower Pulse
Controller
Provides more efficient
blower control, less heat,
increased fuel economy.
Humidity
Sensor
Duty
Signal
A/C
ECU
1
M+
SI
Blower
Pulse
Controller
M
Output
Voltage
(V)
4
M–
3
9
Duty Ratio (%)
Fig. 8-11
752f811
8-10
TOYOTA Technical Training
Air Conditioning: Hybrid Vehicles
Hybrid
System Safety
Hybrid vehicles use a high voltage (HV) battery module to power the
electric motor portion of the power train. Voltage as high as 270 Volts DC
are in the system, do not service a hybrid vehicle unless you are familiar
with the overall operation of the vehicle and the specific operation of the
vehicle system.
To propel the hybrid vehicle and various accessories, power alternates
between the electric motor and gasoline engine at various times. During
repair and service operations, be aware that certain accessories can be
energized even when the engine appears to be OFF and the vehicle is idle.
Troubleshooting/
Self-Diagnosis
Self-Diagnosis
Functions
Similar to conventional HVAC systems on late model Toyotas, the hybrid
A/C ECUs have a self-diagnosis function. The A/C ECU stores operation
failures in memory as a diagnostic trouble code (DTC). DTCs can be
displayed on the multi-display. Since DTCs are stored directly by electric
power from the vehicle battery, they remain in memory even when the
ignition is OFF.
Function
Outline
Indicator Check
Checks mode and temperature setting display
Sensor Check
Checks past and current sensor and A/C inverter
malfunctions, clears past malfunction data.
Actuator Check
Verifies actuators (blower motor, servo-motor, etc.)
are operating correctly according to signals from
the ECU.
TOYOTA Air Conditioning and Climate Control – Course 752
8-11
Section 8
Self-Diagnosis
Procedure
The following is an example of accessing DTC information. On many
hybrid vehicles, DTCs appear on the instrument panel Multi-display.
DTC Retrieval
DTCs appear on
multi-display.
Power switch ON with AUTO
and R/F switches held down.
If both AUTO and R/F switches
are not pressed at the same time.
Indicator Check
(Continuous Operation)
R/F
TEMP
Sensor Check
Actuator Check
(Continuous Operation)
(Continuous Operation)
Fr DEF
Fr DEF
R/F
TEMP
TEMP
Sensor Check
(Stepped Operation)
AUTO
R/F
AUTO
Actuator Check
TEMP
(Stepped Operation)
Fr DEF
Fr DEF
Cancel Check Mode
(Normal operation now Possible)
: Indicates a switch operation
Fig. 8-12
752f812
8-12
TOYOTA Technical Training
TOYOTA AIR CONDITIONING AND CLIMATE CONTROL
WORKSHEET 8-1 (ON-CAR)
Hybrid Air Conditioning System Familiarization
Vehicle:
Year/Prod. Date:
Engine:
Transmission:
Worksheet Objectives:
This worksheet will familiarize you with the operation of the high voltage Electric Inverter A/C compressor and
using the Diagnostic Tester to monitor high and low pressures on the 2004 Prius.
Tools
•
•
•
•
•
and Equipment:
Vehicle
HFC-134a Air Conditioning Refrigerant Recovery and Recharging System
Diagnostic Tester
Repair Manual or TIS
2004 Prius New Car Features Manual
Caution:
This vehicle contains High Voltage components and circuits. Do not touch any High Voltage ORANGE colored
wires or parts. When the “READY” light is illuminated on the combination meter, the internal combustion engine
can start at any time.
Section 1
Electric Inverter A/C Compressor
1. What style compressor is this? ___________________________.
2. What makes the compressor rotate? ________________________________________.
3. What type of refrigerant oil is recommended and why?
__________________________________________________________________________.
4. List the safety precautions to follow when servicing this A/C system:
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
TOYOTA Technical Training
8W1-1
Worksheet 8-1
Section 2
Humidity Sensor
1. What is the purpose of the humidity sensor?
_____________________________________________________________________________
2. Where is the humidity sensor located?
________________________________________________________________________________________
Section 3
Monitor Refrigerant Pressure
1. Switch the A/C system OFF and switch the Power Button OFF.
2. Connect the HFC-134a Air Conditioning Refrigerant Recovery and Recharging Station to the high and
low-pressure service ports.
3. Press the power switch and verify the vehicle is in the READY mode.
4. Connect the Diagnostic Tester to DLC3.
5. Select Active Test and COMPRS TARG SPD. Record the following pressures in the chart below:
a.
Begin at zero and record the refrigerant pressures.
b. Increase the RPM to 4000, then record the system pressures.
c.
Increase the RPM to 6000, then record the system pressures.
Compressor speed:
Low side pressure:
High side pressure
0
4000
6000
Section 4
A/C Data List
1. Select A/C Data List on the Diagnostic Tester. In the User Data menu, select the following items from the
list:
• Evaporator Temp
•
•
•
•
8W1-2
Room Temp
Humidity Sensor
Compressor Speed
Compressor Target Speed
TOYOTA Technical Training
HYBRID AIR CONDITIONING SYSTEM FAMILIARIZATION
a.
What is the relationship between room temperature and the evaporator temperature when the A/C is
OFF and when the A/C is ON?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
b. What happens to the humidity sensor reading when the A/C is switched ON?
_____________________________________________________________________________________________
c.
What happens to the compressor target speed when the humidity sensor and evaporator temperature
sensor values drop?
_____________________________________________________________________________________________
Section 5
Customize Mode
1. The Customize Mode allows modification of certain air conditioning functions to suit the users preference.
Modes are changed using the Diagnostic Tester.
2. Using the Diagnostic Tester, enter the Customize Mode (second screen after switching the tester ON).
3. Select Individual Change. List at least four A/C climate control modes that can be customized:
_________________________________________________________________________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
Note: Return all cars to their original state
Instructor Sign Off: ______________________________________
TOYOTA Technical Training
8W1-3
Worksheet 8-1
Notes
8W1-4
TOYOTA Technical Training
HYBRID AIR CONDITIONING SYSTEM FAMILIARIZATION
Hybrid Air Conditioning System Familiarization
Name: ___________________________________________________________ Date: _________________________
Check each category after participating in the classroom discussion and complete this sheet as you are
completing Worksheet 8-1 using the Hybrid Air Conditioning System Familiarization worksheet in the shop.
Ask the instructor if you have any questions regarding the topics provided below:
I have questions
Topic
I know I can
Comment
Location of major controls
Control of heating and cooling functions
in climate control seat
Control of fan speed in climate
control seat
Location of Peltier device in the seat
TOYOTA Technical Training
8W1-5
Worksheet 8-1
Notes
8W1-6
TOYOTA Technical Training
Glossary of Terms
A
A/C – Air conditioning; a system which dehumidifies and removes heat
from the air.
A/C Inverter – Electronic device in hybrid-powered vehicles. Used to
convert DC voltage to AC to power the electric motor in the Electric
Inverter Compressor.
Ambient Temperature – The temperature of the air around the outside
of the vehicle.
Ambient Temperature Sensor – An NTC-type thermistor. Sends
“temperature” signals to the A/C ECU by the resistance it produces when
heated. Inputs actual outside temperature in front of vehicle for A/C ECU
to factor in cooling output and controls outside temperature indicator on
control panel. Works with vehicle speed sensor and temperature reading
can only go down at stops and not increase until vehicle is in motion.
Amplifier – Sometimes referred to as the A/C ECU. A device that
increases the strength of a signal; in an A/C system, the ECU controls
compressor clutch operation based on various input signals. Also referred
to as “A/C Control Assembly” and “A/C Amplifier.”
ATC (Automatic Temperature Control) – A system that automatically
controls HVAC outlet temperature, distribution pattern and fan speed.
Also called “climate control” or “automatic air conditioning.”
Auto blow-up – the delayed and gentle increase in blower speed upon
initial operation. This reduces the “blast of hot air in the face” tendency
when plastic ducts are still hot and the system is not yet cooling at
maximum efficiency. Some models can use customizing and DATA LIST
feature on Hand-held Tester to test or select this mode. See customization.
B
B+ – Battery voltage, typically controlled by the ignition switch; the positive
terminal of a battery.
Bar – A metric unit for barometric pressure, 1 Bar = 1 kilogram per
square centimeter = 14.5 psig.
Barometric Pressure – “Atmospheric pressure,” pressure exerted on all
surfaces of an object as a result of gravity acting upon the mass of the
atmosphere, typically 14.5 pounds per square inch of gauge pressure (psig).
BEAN (Body Electronics Area Network) – A multiplexing communications
system where multiple signals for various body electrical accessories
travel over a common electrical path.
Blend – A mixture of two or more refrigerant gases intended to replace
some other refrigerant. (Not recommended)
Blower controller – Controls blower motor speed by limiting voltage to
the motor by duty cycle or pulsing current.
TOYOTA Air Conditioning and Climate Control — Course 752
1
Glossary of Terms
Blower resistor – Controls blower motor speed by dropping voltage to
blower motor by in-line resistance.
BTU (British Thermal Unit) – A British unit for measuring the heat energy
of a process. One BTU = the heat energy which raises the temperature of
one pound (one pint) of water by one degree Fahrenheit. One thousand
calories = one KiloCalorie (Kcal).
Bus – A common conductor to which multiple circuits connect in an
electrical system.
C
Calorie – A metric unit for measuring the heat energy of a process; a
common unit for measuring energy (sugar content of food) which will
raise the temperature of one kilogram (one liter) of water by one degree
centigrade. One thousand calories = one KiloCalorie (Kcal).
CAN (Controller Area Network) – A high-speed data multiplex
communication system linking control units and systems.
Capillary Tube – A small passage tube and sensing bulb contains a
refrigerant that expands and contracts according to temperature. The tube
carries the temperature “signal” to the expansion valve.
Celsius – The name of the scientist who devised the metric temperature
scale, see also Centigrade.
Centigrade (° C) – A name for the metric scale of temperature measurement
which is based on the properties of water. Water freezes at 0° C and boils
at 100° C at sea level pressure (1 Bar).
CFC (Chlorine, Fluorine and Carbon) – A family of chemical compounds
also called “chlorofluorocarbons” which are suspected of contributing to a
decline in the stratospheric zone.
R-12 is a CFC. See dichlorodifluoromethane.
Change of State – The process where matter changes from a solid state
to a liquid state or from a liquid state to a gas, usually caused by a great
transfer of heat or a change in pressure.
Charge – The quantity of refrigerant necessary for efficient heat transfer
by an air-conditioning system.
Clutch – A mechanical device for transmitting torque that allows for
engaging and disengaging two shafts or rotating members.
Compressor – A pump that increases the pressure of a gas within a
closed system.
2
TOYOTA Technical Training
Glossary of Terms
Compressor clutch cycling – The compressor clutch normally cycles
only when the system is switched ON or OFF or when evaporator
temperatures sensed by the evaporator thermistor are below the freezing
point. The thermistor signals the ECU/amplifier to disengage the
compressor clutch. Non-cycling will cause evaporator icing. Overly
frequent clutch cycling can be caused by insufficient refrigerant charge
which drops evaporator temperatures.
Condensation – The process where a material changes state from a gas
to a liquid following removal of heat or an increase of pressure.
Condenser – A heat exchanger through which a hot gas passes in order
to remove heat from the gas and causing it to condense into a hot liquid.
Cross-contamination – Mixing of refrigerants or adding aftermarket
replacement refrigerant other than HFC-134a. Refrigerant identifier should
be used on every vehicle before recovering refrigerant from the A/C system
to avoid cross-contamination of service equipment. Refrigerant must be
98-100% HFC-134a to recover and no more than 2% AIR in the system.
Current – A measure of the flow of electrons through an electrical circuit.
The unit of measurement is the “Ampere” or “Amp.” See Ohm’s Law.
Customization/DATA LIST – Feature for some models where the Toyota
Hand-held Tester can display all Auto AC system sensor inputs, air-mix
door positions, actual temperature conditions and other data. Some Auto
switching functions such as switching from RECIRC to FRESH can be
selected or deactivated using the tester.
Cycling – The process of repeatedly turning a control device ON and OFF
based on a prescribed pattern or input signal. See Compressor Clutch
Cycling.
D
DATA LIST – See Customization/DATA LIST
Dehumidifying – The process of removing water vapor (moisture) from
the air; another result of removing heat from the air.
Desiccant – A chemical or structure that absorbs moisture by forming
molecular bonds with water molecules. Located in the receiver-drier or
modulator portion of a subcooling condenser. The moisture absorbed by
the desiccant cannot be entirely removed during evacuation. Thus, the
receiver-drier should be replaced whenever the A/C system is opened to
the atmosphere. HFC-134a and CFC-12 types of receiver-driers must
never be interchanged as they have different desiccant materials. Also
see “receiver-drier.”
Dichlorodifluoromethane – CFC-12 or R-12; a nontoxic, nonflammable
chemical compound of chlorine, fluorine and carbon; a colorless, odorless
gas formerly used as a refrigerant. Replaced in vehicles by HFC-134a
(R-134a).
TOYOTA Air Conditioning and Climate Control — Course 752
3
Glossary of Terms
D.O.T. (U.S. Department of Transportation) – Regulates interstate
transportation of cylinders containing pressurized gas.
DTC (Diagnostic Trouble Code) – Fault codes generated by the ECU
that indicate to service personnel the source of a system malfunction.
A self-diagnosis feature that stores operation failures in memory.
DTCs can be displayed by operating switches on the A/C control panel.
DTCs remain in memory even when the ignition is OFF.
Duct Air Temperature Sensor – Works with solar sensor and ECU to set
outlet temperature toward “face” a bit cooler than the “floor” outlet in
bright sunlight.
Duty cycle – Method of controlling voltage to air mix servos or blower
motors by using a pulsating voltage signal from inside the ECU or
amplifier assembly. See solid state/transistorized.
DVV (Double Vacuum Valve) – Device used on vacuum-controlled ATC
systems to regulate the pressure within the air mix servo-motor in order
to control outlet air temperature.
Dynamic Pressure – The pressures measured from a stabilized and
operating A/C system.
E
Electric Inverter Compressor – Scroll-type compressor found on hybrid
vehicles. Uses a high voltage AC motor to rotate the compressor section
to circulate refrigerant through the A/C system. Speed-controlled by an
A/C ECU.
Equalization of pressures – When the A/C system cycles off, the low and
high sides of the system balance in pressure. This increases the low side
pressure while the high side pressure is reduced. The system does not
balance or equalize immediately due to the restriction of the expansion
valve before the evaporator and the sealing effectiveness of the reed
valves in the compressor. Leak testing with a halogen leak detector is
done with the A/C OFF and with pressures equalized.
Evacuation – The process of removing all gases from a closed system
with a vacuum pump.
Evaporator – A heat exchanger that accepts a spray of hot liquid in order
to absorb heat from air surrounding the evaporator. In this process, the
liquid evaporates and changes into a gas. The ideal temperature of the
evaporator core is near 32° F but not below. Freezing can occur.
Evaporator temperature is controlled by the expansion valve metering
the refrigerant and the thermistor signaling the amplifier (ECU) to switch
the compressor clutch ON and OFF.
Evaporator Temperature Sensor – A thermistor that outputs an electrical
signal according to temperature. This is an input to the A/C ECU, which
controls the A/C compressor clutch in order to prevent evaporator icing
and to regulate cooling temperature output.
4
TOYOTA Technical Training
Glossary of Terms
F
Fahrenheit – The name of the scientist who devised the British temperature
scale in which water freezes at 32° F (0° C) and boils at 212° F (100° C) at
sea level pressure.
Fusible Plug – A special bolt with a hollow center filled with a soft, low
temperature solder. It is designed to melt under high pressure or high
temperature to relieve pressure and protect the system from an explosion.
This item is no longer used. A pressure switch now controls system
pressure by de-energizing the compressor.
Fuzzy Logic – An attempt to duplicate the logic functions of a human
being to automatically control the various functions of the HVAC system.
G
Gaseous – The hottest state of matter in which the material is the least
dense and is able to flow and expand or contract to fill an area. Heat is
absorbed as a liquid changes to a gas.
“Gateway” ECU – A link between systems on a LAN. It connects the
A/C ECU and the rear A/C controls over the AVC-LAN and the rear A/C
amplifier over the BEAN (steering column bus).
H
Heat Energy – The force that changes the measurable heat of an object;
units for heat energy are the BTU and calorie.
Heat Exchanger – A device that allows heat to be transferred between
two liquids or gases without the materials coming into direct contact with
each other.
Heat Load – The total of all sources of energy acting to change the
temperature of an object. Examples are sunlight, ambient temperature
and passenger body temperature.
Heater Core – The heat exchanger that uses engine coolant to heat the
air in the passenger compartment.
High Pressure Side – The section of the refrigerant system between
the compressor and the expansion valve (including condenser and
receiver-drier) where the refrigerant is under high pressure.
Humidity Sensor – Built into some interior air temperature sensors.
The sensor monitors humidity using a resistance film that expands and
contracts according to moisture in the air.
HVAC (Heating, Ventilation and Air Conditioning) system.
Hydrochloric Acid – A mild acid that can erode metal components. It
forms inside an A/C system when hydrogen from water combines with
chlorine from the CFC refrigerant.
Hygroscopic – A property of some liquids to absorb moisture from the air.
TOYOTA Air Conditioning and Climate Control — Course 752
5
Glossary of Terms
I
IDL (Idle) – An input to the ECU when the throttle is at the idle position.
IG (Ignition) – An output signal from the ECU to the ignitor or coil in the
ignition system
Impermeable – A barrier that cannot be penetrated. This refers to
moisture-proof liners in flexible refrigerant hoses.
Inches of Mercury (in. Hg) – A measure of the strength of a vacuum.
This refers to the ability of a vacuum to lift a column of mercury from a
reservoir up a narrow tube.
L
LAN (Local Area Network) – A multiplex path for serial data or a wiring
path that carries more than one signal to a number of different components
in an electrical circuit.
Latent Heat – The additional energy necessary to cause a material to
change state. This is fundamental to efficient heat exchange processes.
Liquid – The middle state between a material being a solid or a gas. A
liquid can flow to fill a space but cannot expand or be compressed.
Lock sensor – Sends compressor rotation signals to the A/C ECU which
then compares compressor speed to engine speed to determine if
compressor has “locked.” ECU then disengages the A/C clutch to prevent
drive belt failure.
Low Pressure Side – The portion of the refrigerant circuit between the
evaporator and the compressor where refrigerant is at a low pressure.
M
Magnetic Valve – An electrically operated solenoid that controls cycling
of evaporators and refrigerant flow in dual A/C systems.
Manifold Gauge – A set of two pressure gauges mounted on a common
valve body. The manifold has two pressure paths that can be connected
together for service operations.
Microbes – Single-cell living organisms (bacteria, mold).
Molecular Sieve – An open-cell structure designed to trap specific
materials or compounds; used as a desiccant in A/C systems.
Multiplex – A method of sending and receiving digital signals through a
single wire conductor. Often used to control satellite control units from a
master ECU.
6
TOYOTA Technical Training
Glossary of Terms
N
Ne – An engine speed input signal to the ECU.
Noncondensable Gas – A gas that cannot be easily condensed into a
liquid state at room temperature; typically refers to air.
Normally Closed – An electrical circuit or component where the path is
connected under “normal” conditions (e.g. engine OFF, cold and stationary
vehicle; a resistance of zero until activated).
Normally Open – An electrical circuit or component where the path is
not connected (open) under “normal” conditions (e.g. engine OFF, cold
and stationary vehicle; a resistance of infinity until activated).
O
O2 (Oxygen) – The naturally occurring molecule made up of two oxygen
atoms, a clear, odorless gas that is crucial to respiration (breathing) of all
animals.
O3 (Ozone) – The molecule made up of three oxygen atoms, a poisonous,
blue gas formed when oxygen is subjected to electrical energy or intense
visible radiation (light).
Oil Separator – Used in scroll-type A/C compressors to prevent excess
refrigerant oil from entering the scroll chambers. Excess oil can damage
the compressor and/or lower the efficiency of the compressor.
Ohm’s Law – A rule which describes the relationship between voltage,
current and resistance within electrical circuits, Voltage = Current X
Resistance.
One-Pass Machine – A machine that recycles refrigerant as it is recovered
from a vehicle A/C system. No additional process is necessary before
returning the refrigerant to service. See also Two-Pass Machine.
Overcharge – Excess refrigerant added to the system beyond specifications
reduces cooling efficiency, creates higher operating pressures and
can damage components and sealing materials. Hot or humid days tend
to increase system pressures. An overcharged system could fail on a
hotter-than-usual day.
Oxygen – The most common element on Earth, present in most organisms
and organic chemicals. Essential to life.
P
PAG (Polyalkylene Glycol) – A synthetic lubricant oil (nonmineral-based)
developed as a substitute for mineral oil for use with HFC refrigerant
R-134a
Performance Test – System operation and cooling performance check.
Uses a thermometer in center dash outlet register and conditions
specified in the Repair Manual (blower fan speed setting, doors open
or closed, engine rpm setting) while checking and other procedures.
Ambient temperature and humidity have a significant affect on
performance test results.
TOYOTA Air Conditioning and Climate Control — Course 752
7
Glossary of Terms
Phosgene (Carbonyl Chloride) – A toxic gas also called “mustard gas”
produced as a byproduct during combustion of CFC-12. Old, flame-type
leak checker is not recommended due to this danger.
Photo-Diode – A single-pole semiconductor which normally blocks the
flow of current in both directions; when subjected to light, it allows the
current to pass in one direction.
Plenum – A chamber common to several passages, as in the central
distribution chamber of a heater blower case or the center passage of a
manifold gauge set.
Power transistor – Controls blower motor speed by limiting the current
to the motor using internal switching circuits to increase resistance and
dissipates heat generated through the cooling fins on the case.
PSI (Pounds Per Square Inch) – A British unit of measure for fluid or gas
pressure where zero psi is the absolute vacuum of outer space.
PSIG (Pounds Per Square Inch Gauge) – A measurement of fluid or gas
pressure in which zero psi on the gauge is equal to atmospheric pressure
or 14.5 pounds per square inch.
PTC (Positive Temperature Coefficient) – Describes the relationship
between temperature and resistance of common metals.
PTC Heater Core – High efficiency heater core containing a Positive
Temperature Coefficient (PTC) heating element. Used to create warm
interior air before engine coolant is able to transfer heat to the heater
core. Current passing through PTC element creates heat to warm air
passing over it.
R
R-12 – See dichlorodifluoromethane.
R-134a – See tetrafluoroethane.
Radiator – A water-to-air heat exchanger, the final stage cooler of an
engine-cooling system.
Receiver-Drier – A combined accumulator and dehydrator in a refrigeration
system. Filters impurities from the liquid refrigerant. Also see “desiccant.”
HFC-134a and CFC-12 receiver-driers are not interchangeable
Recharging – Filling an A/C system following repair with a quantity of
refrigerant necessary for efficient heat transfer.
Recirculate – Recooling of air in an enclosed space, providing increased
cooling efficiency.
Reclamation – An off-site process of purifying recovered refrigerant to an
“as-new” condition.
Recovery – Removal of refrigerant from an A/C system before repair or
service.
8
TOYOTA Technical Training
Glossary of Terms
Recycling – On-site purification of recovered refrigerant to a standard as
defined by the SAE.
Refrigerant – A substance used in a heat exchange system to cool an
area based on evaporation and condensation of the refrigerant.
Relative Humidity – A measure of the amount of water vapor in
suspension in the atmosphere at a given temperature.
Relief Valve – A nonreusable valve that opens to relieve excessive pressure
and thus protect the system from explosion without a total loss of
refrigerant; replaces the fusible plug on newer A/C systems.
Resistance – A measure of an electrical circuit or a component to resist
current flow. See Ohm’s Law.
Retrofit – Replacement A/C system components installed on a vehicle
in service using non-CFC refrigerant. There are kits available to convert
vehicles using R-12 refrigerant to HFC-134a. Usually consists of new
HFC-134a fittings, receiver-drier and system identification decals.
S
SAE (Society of Automotive Engineers) – A professional organization that
drafts standards for vehicle systems.
Saturated – 100% relative humidity, air is saturated when it holds the
maximum possible amount of water vapor in suspension, water will
precipitate (condense into liquid and fall out of suspension) at this point.
Sensing Bulb – A small chamber filled with refrigerant and connected to
the expansion valve by a thin capillary tube, controls expansion valve
operation based on the surface temperature at the outlet of the evaporator.
Series Resistance – An electrical circuit where the current flows through
the system components in a single path between power and ground.
See Ohm’s Law.
Sight glass – Small glass viewing window near receiver-drier or pressure
switch in the high-pressure side of the A/C system. Can be helpful for
diagnosis if excessive bubbles or foreign material are seen circulating in
the system. Actual charge amount must be determined using a refrigerant
charging station that uses a scale to accurately measure the refrigerant
amount. Using the sight glass to determine the charge is incorrect and
will result in an improper charge amount and poor cooling.
Sludging Valve – Used in through-vane A/C compressors. This valve
prevents damaging the through-vanes or the reed valve by allowing liquid
oil to escape from the compression area into an oil chamber.
Solar Sensor – Detects sun load which is 60% of heat entering the vehicle
and provides input information to the ECU.
TOYOTA Air Conditioning and Climate Control — Course 752
9
Glossary of Terms
Solid – The coldest of the three states of matter, a solid does not flow
to fill a space and cannot be compressed or expanded.
Solid state/transistorized – Electronic components using transistors
to control current flow to components such as the blower motor or
servo-motors to control their operation.
Speed Sensor – An input sensor to the A/C ECU or amplifier to prevent
ambient temperature sensor from giving false indications when not
moving such as stopped at signal.
SPD (Speed) – A variable input signal to the ECU representing vehicle
road speed. See Speed Sensor.
STA (Start) – An input signal to the ECU when the starter solenoid is
energized.
Stabilize – The steady operating condition of an A/C system during heat
exchange and pressures and temperatures are within normal operating
range.
Static Pressure – The steady pressure within an A/C system that is not
operating, units are in PSIG or kg/cm.2
Step-less – Variable blower fan speed control as opposed to 3 or 4 set
fan speeds.
Stratosphere – A layer of the Earth’s atmosphere 12-20 miles above the
Earth.
Stratospheric Ozone – A layer of ozone gas (O3) surrounding the Earth in
the stratosphere. Because ozone is blue in color, this layer reflects much of
the ultraviolet light from the sun to protect the surface from the radiation.
Systematic – An approach to problem-solving based on a logical process.
T
TAM – Ambient air temperature or outside air temperature measured in
the front grille area.
TAO – Outlet air temperature sensor in Auto A/C sends signal to A/C ECU.
Temperature – A measure of the heat quantity present in a material,
units are Fahrenheit (English system) or Centigrade (Metric system).
Tetrafluoroethane – HFC-134a or R-134a; a molecule of hydrogen, carbon
and fluorine, a clear, odorless, nontoxic gas, a refrigerant for mobile air
conditioning systems which has greatly reduced potential to deplete ozone
and a low potential for contributing to global warming.
THA – a variable input signal to the ECU that represents air temperature
in the air intake passage.
Thermal Capacitance – The ability of a material to resist sudden
temperature changes, describes an insulating property.
10
TOYOTA Technical Training
Glossary of Terms
Thermistor – A solid-state component that changes resistance with
changes in temperature. Used as an electrical thermal sensor. A thermistor
has a negative temperature coefficient.
THW – An input signal to the ECM/ECU that represents coolant
temperature at the cylinder head outlet.
TR (Room Temperature Sensor) – Measures interior temperature.
TSET (Temperature Setting) or target temperature – Selected with Auto
A/C systems input to A/C ECU.
Two-Pass Machine – Recovers refrigerant from a vehicle system without
recycling. An additional process is necessary before the refrigerant can
be returned to service. See also One-Pass Machine.
U
UL® (Underwriters’ Laboratory) – An independent organization that tests
products to verify compliance with safety standards.
Ultraviolet Radiation – Intense blue light that consists of visible and
invisible wavelengths. Excessive ultraviolet radiation may cause skin
cancer, cataracts and other harm to living things.
V
Vacuum – An extremely low pressure, the absence of any measurable
pressure.
Vaporization – A process where a liquid changes into a gas, either due to
a drop in pressure or an increase in temperature.
Voltage – A measure of the electrical potential of a circuit, voltage drop
within a circuit is defined by Ohm’s Law. See also Ohm’s Law.
VTA – A variable input signal to the ECM/ECU that corresponds to the
angle of the throttle opening.
W
Water Control Valve – A water regulation control valve that controls
coolant flow into the heater core. It is controlled by a cable or a servo-motor
for outlet temperature control. Fully closed on MAX COLD setting but
opens in incremental steps when selecting higher temperature settings.
Controlled by cable manually on older models; by servo motor on newer
models. If sticking open or closed, can cause reduced heating or cooling
complaint.
TOYOTA Air Conditioning and Climate Control — Course 752
11
Glossary of Terms
12
TOYOTA Technical Training