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Air Conditioning Compressor Malfunction



Air Conditioning Compressor Malfunction (RPO LS4 - 5.3L)

Diagnostic Instructions

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



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 engine control module (ECM) to ground the A/C compressor clutch relay control circuit, which will switch the A/C COMP 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 4,760 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.



Reference Information
Schematic Reference

HVAC Schematics (HVAC - Automatic)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

* Air Temperature Description and Operation (Air Temperature Description and Operation)
* Air Delivery Description and Operation (Air Delivery Description and Operation)

Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for Scan Tool Information


Circuit/System Verification

1. Ignition ON, engine running.
2. Press the A/C request switch. The A/C compressor clutch should engage.
3. Place the mode switch in the defrost position. The A/C compressor clutch should engage.



Circuit/System Testing

1. Ignition OFF, disconnect the A/C COMP relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal and ground.

• If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the ignition circuit terminal and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test or replace the A/C COMP relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal for a short to ground.

5. Disconnect the harness connector at the A/C compressor clutch.
6. Test for less than 1.0 ohm of resistance between the A/C compressor clutch ground circuit terminal A and ground.

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

7. Connect the harness connector at the A/C compressor clutch.
8. Connect a 10A fused jumper wire between the B+ circuit terminal and the control circuit terminal. Verify the A/C compressor clutch is activated.

• 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 clutch.

9. Connect a test lamp between the ignition circuit terminal and the control circuit terminal.
10. Command the A/C relay 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.

11. If all circuits test normal, test or replace the A/C COMP relay.



Component Testing


Relay Test
1. Ignition OFF, disconnect the A/C COMP relay.
2. Test for 60-180 ohms of resistance between terminals 85 and 86.

• If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87


• If not the specified value, replace the relay.

4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.

• If greater than the specified range, replace the relay.




Repair Instructions

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

* Compressor Clutch Assembly Replacement (Service and Repair)
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Control Module References (Programming and Relearning) for ECM setup, replacement, and programming


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