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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.

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

1. 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.

• If the clutch does not engage refer to Air Conditioning (A/C) System Performance Test (Short Wheel Base) Air Conditioning (A/C) System Performance Test (Long Wheel Base - 1500 Series) Air Conditioning (A/C) System Performance Test (Long Wheel Base - 2500 Series) Initial Inspection and Diagnostic Overview Initial Inspection and Diagnostic Overview Initial Inspection and Diagnostic Overview

Circuit/System Testing

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

• If greater than the specified, 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 B.
7. Ignition OFF test for less than 1.0 ohm of resistance between the A/C compressor ground circuit terminal A 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 63. 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 Replacement (LY2, LY5, LH6, L76, L92 and LMG) Compressor Replacement (HP2)
* Compressor Clutch Plate/Hub Assembly Replacement
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