SYSTEM
CONTROLS
CHAPTER 10
CBC AUTO
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OBJECTIVES
• Discuss Operation and Function of controls for Manual
and Automatic Climate Control System.
• Discuss controlling system temperature by temperature
and pressure actuated controllers.
• Discuss High and Low pressure switches and controls.
• Understand how to trace air conditioning electrical
schematics
• Understand vacuum system operation
• Describe the different types of evaporator blower
motors.
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SIMPLE CONTROL SYSTEM
• ONE WIRE FEEDS ALL PARTS
• CONSISTS OF MASTER ON/OFF
SWITCH
• BLOWER CONTROL
• THERMOSTAT
• BLOWER MOTOR
• CLUTCH COIL
• CIRCUIT PROTECTION DEVICES
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PAGE 189C
JH
COMPLEX CONTROL
SYSTEM
• The more features the more complex the
a/c system controls are.
• Usually shares fuses and circuit breakers
with other systems
• Sometimes other system may be shown
on the electrical schematic
Page 190C
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Page 241L
Page 243L
page 214C
MASTER CONTROL HEAD
• Contains:
– Blower control
Switch
– Temperature control
– Mode control
– Digital readout
• Schematic sometimes
shows components
separately
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Page 197C
BLOWER MOTORS
• All blower motors use a squirrel cage to move
air
• Some motors have several windings (197C)
• Must make sure replacement motor is correct
• Can test with ohmmeter or ammeter
• Motor can be on ground side or feed side of
circuit
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SQUIRREL CAGE
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Page 197C
JH
BLOWER MOTOR &
HOUSING
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Page 197C
JH
Page 247L
COMPRESSOR CLUTCH
• Electromagnetic action
• Controlled by thermostat or pressure
cycling switches
• System components protected by
dumping diode across clutch coil
• To test you must use ohmmeter or
ammeter.
• Clearance will affect amperage draw
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COMPRESSOR DISCHARGE
PRESSURE SWITCH
• High Pressure Cutoff
Switch
• Usually located in
high pressure lines or
on compressor
• Not resettable, must
replace
• 300-500 PSI
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Page 201C
JH
Low Pressure Switch
• Can be used to shut
off compressor clutch
• Can be used to cycle
clutch (dual function)
• Found on low side or
high side of system
• Can apply pressure
to test using
voltmeter or
ohmmeter
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page 200C
JH
COOLANT TEMPERATURE
WARNING SYSTEMS
• Coolant system affect
A/C operation
• One lamp coolant
warning switch
• Two lamp coolant
lamp warning switch
• Some don’t come on
until 220 to 250
degrees
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CONTROL DEVICES
• Actuators are either electrical or vacuum
operated
• A/C system must have strong supply of
vacuum to operate all the actuators in the
system
• Sometimes must use motor operated vac
pump or engine to test vacuum devices
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Page 206C
VACUUM CIRCUIT SOURCE
207C
207C
• Has check valve so vacuum maintained in
system when going up hill
• Hoses color coded sometimes
• Must trace out like electrical.
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Page 206C
Single Action Vacuum Motor
•
•
•
•
Only operates with one vacuum source.
Vacuum only pulls in one direction.
Can test with hand held vac pump
Used to control doors
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Page 206C
Dual Chamber Vacuum Motor
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INPUTS
AUTOMATIC
TEMPERATURE
CONTROLS
256L
OUTPUTS
218C
218C
220C
214C
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Page 213C
JH
Page 219C
ASPIRATOR
• Common Input Sensor on EATC
• Monitors in-car temperature
• Broken hose is a common problem
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AUTOMATIC A/C
214C
CBC AUTO
215C
221C
PAGE 213C
JH
School Work!!!!!
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