Air Conditioning Compressor Malfunction

Air Conditioning Compressor Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.

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. 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 less than 4760 RPM.
* Engine speed is more than 600 RPM.
* A/C high side pressure is between 2929-269 kPa (425-39 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.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector X2, terminal 8 ground circuit terminal at the HVAC control module.
2. Test for less than 1.0 ohm of resistance between the ground circuit terminal 2 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Remove the A/C compressor clutch relay.
4. Verify that a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

5. Verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.

• If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance. If the A/C clutch fuse is open, test the relay switch control circuit for a short to ground. If all circuits test normal, test or replace the A/C compressor clutch.

6. Disconnect the harness connector at the A/C compressor clutch terminal 1.
7. Ignition OFF test for less than 1.0 ohm of resistance between the A/C compressor ground circuit terminal 2 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

8. Connect the harness connector at the A/C compressor clutch.
9. Connect a 10-amp fused jumper wire between the relay switch B+ circuit terminal 30 and the relay switch control circuit terminal 87. Verify the A/C compressor clutch engages.

• If the A/C compressor clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C compressor.

10. Connect a test lamp between the relay control circuit terminal 86 and the relay coil B+ circuit terminal 85.
11. Using a scan tool, command the A/C relay output ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp remains ON all the time, test for a short to ground on the control circuit connector X1 terminal 53. If the circuit tests normal, replace the ECM.
• If the test lamp remains OFF all the time, test for a short to voltage or an open/high resistance on the control circuit. If the circuit tests normal, replace the ECM.

12. If all circuits test normal, test or replace the A/C compressor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Compressor Clutch Assembly Replacement
* Air Conditioning Compressor Replacement (LS4) Air Conditioning Compressor Replacement (LZE, LZ4, LZG)