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Air Conditioning Compressor Malfunction



Air Conditioning Compressor Malfunction

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 assembly sends a GMLAN message to the Engine control module (ECM) for an A/C request. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C CMPR 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 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) Air Conditioning (A/C) System Performance Test (LH2 w/ Heavy Duty Cooling) (Initial Inspection and Diagnostic Overview)Air Conditioning (A/C) System Performance Test (LH2 w/ Standard Cooling) (Initial Inspection and Diagnostic Overview)Air Conditioning (A/C) System Performance Test (LY7 w/ Heavy Duty Cooling) (Initial Inspection and Diagnostic Overview)Air Conditioning (A/C) System Performance Test (LC3) (Initial Inspection and Diagnostic Overview)Air Conditioning (A/C) System Performance Test (LY7 w/Standard Cooling) (Initial Inspection and Diagnostic Overview)
.
* 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).



Reference Information
Schematic Reference

HVAC Schematics (Electrical Diagrams)
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

Engine running, press the A/C request switch. The A/C compressor clutch should engage.


Circuit/System Testing

1. Ignition ON, with a scan tool, verify the A/C Switch parameter cycles between On and Off with each press of the A/C switch

• If the parameter does not cycle, replace the HVAC control module.

2. Remove the A/C CLTCH relay.
3. Verify that a test lamp illuminates between the 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.

4. Verify that a test lamp illuminates between the 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.

5. Disconnect the harness connector at the A/C compressor clutch.
6. Ignition OFF test for less than 1.0 ohm 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.

7. Connect the harness connector at the A/C compressor clutch.
8. Connect a 10A fused jumper wire between the 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.

9. Connect a test lamp between the relay control circuit terminal 86 and the B+ circuit terminal 85.
10. 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.

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



Repair Instructions

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

* Air Conditioning Compressor Replacement (LH2) (Service and Repair)Air Conditioning Compressor Replacement (LY7) (Service and Repair)
* Compressor Relay Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for HVAC control module and ECM replacement, setup, and programming


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