REFRIGERATION SYSTEM
Chapter 4
 Classroom Manual
 Page 67

OBJECTIVES
Diagnose six system malfunctions by gauge
readings.
 Identify the low and high side of the air
conditioning system.
 Read and understand temperature-pressure
charts.
 Discuss temperature-pressure relationships.

OBJECTIVES
Identify differences between CFC-12
and HFC-134a systems.
 Identify differences between
thermostatic expansion valve (TXV) and
fixed orifice tube (FOT) systems.
 Understand the proper handling of
refrigerants and refrigeration oil.

INTRODUCTION
Figure 4-1, (Pg 68C) shows the dividing
line between low and high sides.
 Low side gauge is a compound gauge.
 There is a direct relationship between
pressure and temperature.
 Air temp flowing through evaporator will
be a few degrees warmer than the
freon.

A
C
S
Y
S
T
E
M
Low side
Expansion Valve
High side
SYSTEM DIAGNOSIS
Knowing the ambient air temperature.
 Determine normal HIGH side pressure.
 There are seven conditions for A/C
systems.
 1 normal condition.
 6 conditions that indicate a malfunction.

NORMAL OPERATION

Low-side gauge: Normal pressure
– CFC-12: 32-33 PSI
– HFC-134a: 30-31 PSI

High-side gauge: Normal pressure
– CFC-12: 185-190 PSI
– HFC-134a: 204-210 PSI
PLATE 1
Normal
refrigerant
charge
expansion
valve system.
 Receiver/
Dryer in high
side of system.

PLATE 9
Normal
refrigerant charge
orifice tube
system.
 Accumulator in
low side.

REFRIGERANT
Refrigerant is the term used when
referring to the fluid that is used in an
automotive air conditioning system.
 “a gas used in a mechanical
refrigeration system”

page 77
R-12 (CFC-12)
Dichlorodifluoromehtane is CFC-12
 Safe to Humans
 Can withstand high pressures without
decomposing or deteriorating
 Boiling Point is -21.67 degree
Fahrenheit
 Does not react with A/C components
 Soluble in mineral oil

Temperature and Pressure
Relationship of CFC-12
Freon temperature and degrees
Fahrenheit are roughly the same from
20 to 70 degrees.
 A gauge reading of 28 PSI equals a
refrigerant temperature of 30 degrees.

page 78
134a
New Refrigerant to replace CFC-12.
 Tetrafluoroethane (R-134a)
 Is a hydroflourocarbon (HFC)
 Does not contain chlorine.
 Molecules are 11 times smaller so must
use barrier type refrigerant hoses.

page 78
R-22 for LEAK TESTING
R-12 = 50psi
 R-22 = 100psi
 Do NOT mix refrigerants
 R-22 is NOT a replacement for R-12
 Small amounts of R-22 used in leak
testing can be vented to atmosphere.

page 82
HANDLING REFRIGERANTS
All refrigerants must be properly stored,
handled, and used.
 Do NOT expose containers to flame.
 Burning refrigerant creates poisonous gas.
 Pound cans can NOT be identified by color.
 Do NOT mix refrigerants.

page 82
SAFETY PRECAUTIONS
Wear safety glasses or goggles at all
times.
 Do NOT vent freon in a confined space.
 Avoid breathing these or any other fumes.
 HFC-134a is combustible.
 Do NOT pressure test A/C system with
shop air.

page 84
OTHER REFRIGERANTS
Use R-12 in R-12 systems.
 Use R-134a in R134a systems.
 R134a is the only legal replacement for
R-12 after proper retrofit procedures.

page 86
REFRIGERATION OIL
R-12 uses mineral oil.
 R134a uses PAG oil.
 Ester Oil can be used in conversions.
 Small Quantities of Mineral oil can be
mixed with Ester oil.
 Mineral oil and PAG oil are not mixable.

page 86
SERVICING TIPS
A/C oil level should be checked each
time the system is drained.
 Keep the cap on oil container.
 Refrigerant oil is hygroscopic.
 Moisture is damaging to A/C system.

PREVENTIVE
MAINTENANCE
Inspect electrical system for A/C
 Inspect Blower motor for abnormal
noises, leaves in ducts, etc..
 Check Voltages
 Check Compressor Clutch operation
 Check Belts and A/C Hoses
 A/C Function Check

page 88