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Troubleshooting
The dash A/C and Heat system uses a
combination of compressed air (developed by
the chassis system), vacuum air (developed by
the vacuum generator) and electric relays and
vacuum switches. Therefore, any repair can be
classified in one of five categories:
Electrical
Vacuum
Air Conditioner
Heater
Defroster
No Cooling:
Check that the blower is operating, A/C
switch is in A/C or MAX A/C position,
temperature control is turned to MAX
cooling (blue area).
System fuses are not blown.
Condenser fan is operating.
Check power supply to unit and
grounding of system.
Check wiring.
Coolant valve is leaking.
Drive belt is loose or broken.
Compressor Clutch is inoperative, will
not engage.
Expansion Valve is faulty or frozen.
Thermostat control is faulty.
Mode control switch is faulty.
Compressor is faulty.
Loss of refrigerant.
NOTE
An ultraviolet or UV Blue Light cube
is used for leak detection when dye is
introduced to the A/C System.
19
Reduced Cooling:
Coolant valve not operating correctly.
Air passages are obstructed.
Loose or worn drive belt.
Check blower and select switch.
Thermostat control valve is faulty.
Expansion valve is faulty.
Compressor is faulty.
Low refrigerant charge.
No Heating:
A/C switch is turned off.
Blower switch is turned off.
Verify the proper engine coolant level.
Verify that the engine is reaching
operating temperature.
Verify engine coolant is reaching water
valve attached to unit.
Verify operation of water valve to
permit engine coolant to pass through
valve to heater core.
Check unit fuses.
Check power supply to water valve and
grounding.
Check wiring.
Engine thermostat faulty.
Blower Does Not Operate or Runs Slow:
Check fuses.
Check for loose or corroded
connection.
Check wiring.
Check to ensure ignition switch is on.
Check blower and select switch.
Motor shaft has seized.
Blower wheel is out of alignment.
Damper Doors Do Not Operate:
Is the vacuum generator being powered
and producing a vacuum?
Check the vacuum line entering the
unit for vacuum.
Check that the vacuum solenoid
mounted on unit is receiving power
from the mode switch. If operating
properly, the vacuum solenoid will feel
hot if current is engaging the solenoid.
Check the mode switch.
Check wiring.
Check for a pinch in the vacuum line
leading to the vacuum motor that
operates the damper door in question.
DIAgNOSTIc pLUg LOcATION
The diagnostic
plug is located under
the dash on the left
side of the steering
column. Through
this plug, ABS, engine and transmission
systems communicate over SAE J1939
electronic technology. J1587 is used to retrieve
diagnostic codes from a particular system,
such as the engine for example.
Engine Diagnostics:
The engine diagnostics will notify the
operator of deviations from the programmed
limits of the engine through the Warning"light
on the standard dash or Check Engine light on
the optional dash. Should a system component
with the engine develop a deviation, the
Warning light or Check Engine light will
illuminate and a diagnostic code will be logged
and stored in the system memory. These codes
are accessed by a service technician using
special equipment.
090280e
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Troubleshooting
