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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, 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.

• If the clutch does not engage refer to A/C compressor clutch

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the A/C low pressure switch.
2. Test for less than 5 ohms between the ground circuit terminal B and ground.

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

3. Ignition ON, verify the scan tool Low Pressure Switch parameter is Open.

• If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC control module

4. Connect a 3-amp fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool Low Pressure Switch parameter is Closed.

• If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module

5. Connect the harness connector at the A/C low pressure switch. Verify the scan tool Low Pressure Switch parameter is Closed.

• If not the specified value, test or replace the A/C low pressure switch.

6. Ignition OFF, disconnect the A/C relay.
7. 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.

8. 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.

9. 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.

10. Disconnect the harness connector at the A/C clutch coil.
11. Test for less than 1 ohm between the ground circuit terminal 2 and ground.

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

12. Connect the harness connector at the A/C clutch coil.
13. 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.

14. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
15. 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.

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

Repair Instructions

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

* Air Conditioning Compressor Replacement (LY2, LY5, LH6, L76, L92 and LMG) Air Conditioning Compressor Replacement (LLY/LMM) Air Conditioning Compressor Replacement (LU3)
* Compressor Clutch Plate/Hub Assembly Replacement (4.3L, 6.6L) Compressor Clutch Plate/Hub Assembly Replacement (V8 - Gas)
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