Air Conditioning Compressor Malfunction
Diagnostic Instructions
Diagnostic Fault Information
Circuit/System Description
When the A/C switch is pressed, the HVAC control module grounds the A/C request signal circuit. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C CMPRSR CLUTCH relay on. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.
Diagnostic Aids
The following conditions must be met in order for the ECM to turn on the
compressor clutch:
- Battery voltage is between 9-18 volts
- Engine coolant temperature (ECT) is less than 123°C (253°F)
- Engine speed is greater than 600 RPM
- Engine speed is less than 4,760 RPM
- A/C high side pressure is between 2929-269 kPa (39-425 psi)
- Throttle position is less than 100 percent
- Evaporator temperature is greater than 0°C (32°F)
- ECM does not detect excessive torque load
- ECM does not detect insufficient idle quality
- The ambient temperature is above 1°C (34°F)
Circuit/System Verification
- Engine running, press the A/C request switch. The A/C compressor clutch should engage.
- Place the mode switch in the defrost position. The A/C compressor clutch should engage.
¤ If the clutch does not engage refer to A/C compressor clutch
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the A/C low pressure switch.
- Test for less than 5 ohms between the ground circuit terminal B and ground.
¤ If greater than the specified range, test the ground circuit for an open/high resistance.
- Ignition ON, verify the scan tool Low Pressure Switch parameter is Open.
¤ If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC control module
- Connect a 3-amp fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool Low Pressure Switch parameter is Closed.
¤ If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module
- Connect the harness connector at the A/C low pressure switch. Verify the scan tool Low Pressure Switch parameter is Closed.
¤ If not the specified value, test or replace the A/C low pressure switch.
- Ignition OFF, disconnect the A/C relay.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground.
¤ If the test lamp illuminates, test the control circuit for a short to voltage.
- Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.
¤ If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance. If the circuit tests normal and ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.
- Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground.
¤ If the test lamp does not illuminate, test the B+ circuit for a short to ground or a open/high resistance. If the circuit tests normal and B+ circuit fuse is open, replace the A/C clutch relay.
- Disconnect the harness connector at the A/C clutch coil.
- Test for less than 1 ohm between the ground circuit terminal 2 and ground.
¤ If greater than the specified range, test the ground circuit for an open/high resistance.
- Connect the harness connector at the A/C clutch coil.
- Connect a 10-amp fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87. Verify the A/C clutch is activated.
¤ If the A/C clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C clutch.
- Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
- Command the A/C relay output function ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
¤ If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. ¤ If the test lamp is always OFF, test the control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.
- If all circuits test normal, test or replace the A/C clutch relay.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
See: A L L Diagnostic Trouble Codes ( DTC )\Testing and Inspection\Verification Tests
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