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Air Conditioning Compressor Malfunction




Air Conditioning Compressor Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (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 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 2°C (34°F)
* ECM does not detect excessive torque load
* ECM does not detect insufficient idle quality
* The ambient temperature is above 1°C (34°F)

Reference Information
Schematic Reference

HVAC Schematics (HVAC - Manual)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

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

Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Control Module References) for scan tool information

Circuit/System Verification

1. Engine running, press the A/C request switch. The A/C compressor clutch should engage.
2. Place the mode switch in the defrost position. The A/C compressor clutch should engage.

Circuit/System Testing

Note: Before executing Circuit/System Testing, all conditions shown in Diagnostic Aids must be met.

1. Ignition OFF, disconnect the A/C relay.
2. 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.

3. 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.

4. 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.

5. Disconnect the harness connector at the A/C clutch coil.
6. Test for less than 10 ohms between the ground circuit terminal 2 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 clutch coil.
8. 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.

9. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
10. 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.

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

Repair Instructions

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

* Air Conditioning Compressor Replacement (LU3) (Air Conditioning Compressor Replacement)Air Conditioning Compressor Replacement (LGH, LML) (Air Conditioning Compressor Replacement)Air Conditioning Compressor Replacement (LZ1, L20, LC9, L9H, L92, LMG) (Air Conditioning Compressor Replacement)Air Conditioning Compressor Replacement (HP2) (Air Conditioning Compressor Replacement)
* Compressor Clutch Plate/Hub Assembly Replacement (Service and Repair)
* Control Module References (Control Module References) for HVAC control module and ECM replacement, setup, and programming

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