Service Manual

5-38 627333-A
HVAC Testing and Adjusting
Troubleshooting Using Active
Diagnostics
Several systems can be checked with active
diagnostics.
Checking Temperature Sensors
Use following procedure to verify temperature sensor
readings:
• CAB - Cab air temperature
• DUCT - Duct air temperature
• EUAP - Evaporator core temperature (Switch)
• DOOR - Mode Door Actuator Feedback Position
1. Measure temperature near sensor being checked.
2. Enter active troubleshooting. Refer to Entering
Active Troubleshooting for instructions about active
troubleshooting.
3. CAB is first code displayed, continue to sensor
being verified. Displayed temperature should be
near reading of thermometer.
4. If temperatures are not similar, verify the following:
• Accuracy of thermometer.
• Wiring connections for temperature sensors in
cab.
• Check displayed temperature for other modes
to verify control module is not faulty.
• If all temperature sensors display −54 degrees
C (−65 degrees F), replace HVAC control
module.
• Check power to control module.
• Check serial communications between control
panel and control module for damage.
• Check for poor wire connections.
5. Probable Solutions
• Repair faulty wire connections.
• Replace temperature sensor and verify proper
operation.
• Replace control module and verify proper
operation.
Checking Compressor Clutch
Use the following to verify operation of compressor
clutch:
NOTE: Test should be performed in air temperatures
greater than 21 degrees C (70 degrees F),
clutch may not engage below that temperature.
If necessary, use a heat source to warm outside
air temperature.
1. Move mode control switch to DEFROST.
2. Enter active troubleshooting. Refer to Entering
Active Troubleshooting for instructions on active
troubleshooting.
3. CAB is first code displayed. Continue to switch
being verified. Display should be A-C for
compressor clutch.
4. Compressor clutch should be engaged in defrost
mode and LED display should display ON. This
indicates compressor clutch is on.
NOTE: Test should be performed in air temperatures
greater than 21 degrees C (70 degrees F),
clutch may not engage below that temperature.
If necessary, use a heat source to warm outside
air temperature.
5. If LED display shows OFF verify the following:
• Outside temperature is at least 21 degrees C
(70 degrees F).
• Verify refrigerant charge present in A/C system.
• Verify connections to refrigerant pressure
switches, refer to Checking Refrigerant
Pressure Switches for additional information.
• Verify all wire connections.
6. If no other problems can be found and display
shows OFF, replace control module.
7. If LED shows ON, but clutch does not engage,
verify:
• Check voltage supplied to compressor clutch.
• Verify wire connection at compressor clutch.
• Verify wire connection at relay in HVAC unit.
8. If display shows ON and compressor clutch is not
receiving 12 volts, replace control module.
9. If proper voltage is being supplied to compressor
clutch but compressor clutch does not engage,
replace compressor clutch.