GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    â€¢  Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    â€¢  Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    â€¢  Diagnostic Procedure Instructions provides an overview of the diagnostic category.

DTC Descriptors

DTC P1546: Air Conditioning Compressor Feedback Circuit Low

DTC P1539: Air Conditioning Compressor Feedback Circuit High

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

A/C Compressor Clutch Feedback

P1546

P1546

P1539

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Circuit/System Description

The A/C compressor clutch relay is monitored by the ECM/PCM through the A/C compressor clutch relay feedback circuit.

Conditions for Running the DTC

    â€¢ Engine is running.
    â€¢ Any of the conditions for setting the DTC are met for 15 seconds.
    â€¢ Battery voltage is between 11-18 volts.

Conditions for Setting the DTC

The ECM/PCM detects that the A/C compressor clutch is not on after an A/C request has been made.

Action Taken When the DTC Sets

    â€¢ The ECM will not illuminate the malfunction indicator lamp (MIL)
    â€¢ The ECM stores the Failure Records.
    â€¢ The A/C compressor clutch is disabled.

Conditions for Clearing the DTC

    â€¢ The history DTC will clear after 40 consecutive ignition cycles have occurred without a malfunction.
    â€¢ The DTC will become history if the ECM no longer detects a failure.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

    â€¢  Air Temperature Description and Operation
    â€¢  Air Delivery Description and Operation

Electrical Information Reference

    â€¢  Circuit Testing
    â€¢  Connector Repairs
    â€¢  Testing for Intermittent Conditions and Poor Connections
    â€¢  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

  1. Ignition ON, observe the scan tool A/C Request Signal parameter while changing the mode switch from OFF to Defrost, the reading should change from No to Yes.
  2. ⇒ If the reading does not change while switching between the commanded states, refer to A/C Request Malfunction.
  3. Observe the scan tool A/C Compressor Cycling Switch parameter. The reading should be normal.
  4. ⇒If not the specified value, refer to Low Pressure Switch Malfunction.
  5. Command the A/C relay ON and OFF with a scan tool. Observe the A/C compressor operation, the A/C compressor clutch should engage and disengage when changing between the commanded states.
  6. ⇒If the A/C compressor does not engage or does not disengage, refer to A/C Compressor Malfunction.

Circuit/System Testing

A/C Request Malfunction

  1. Ignition OFF, disconnect the harness connector at the A/C high pressure switch.
  2. Ignition ON, mode set to Defrost, verify that a test lamp illuminates between the control circuit terminal B and ground.
  3. ⇒If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal refer to Blower Motor Malfunction .
  4. Verify the scan tool A/C Request Signal parameter is No.
  5. ⇒If not the specified value, test the signal circuit terminal A for a short to voltage. If the circuit tests normal, replace the ECM/PCM.
  6. Install a 3A fused jumper wire between the signal circuit terminal A and the control circuit terminal B. Verify the scan tool A/C Request Signal parameter is Yes.
  7. ⇒If not the specified value, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM/PCM.
  8. If all circuits test normal, test or replace the A/C high pressure switch.

Low Pressure Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the A/C low pressure switch.
  2. Test for less than 1 ohm between the ground circuit terminal A and ground.
  3. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  4. Verify the scan tool A/C Compressor Cycling Switch parameter is Normal.
  5. ⇒If not the specified value, test the signal circuit terminal B for short to ground. If the circuit tests normal, replace the ECM/PCM.
  6. Install 3A fuse jumper between the signal circuit terminal B and the ground circuit terminal A. Verify the scan tool A/C Compressor Cycling Switch parameter is Low Pressure.
  7. ⇒If not the specified value, test the signal circuit for short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM/PCM.
  8. If all circuits test normal, test or replace the A/C low pressure switch.

A/C Compressor Malfunction

  1. Ignition OFF, disconnect the A/C compressor clutch relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
  3. ⇒If the test lamp illuminates, test the control circuit for a short to voltage.
  4. Verify that a test lamp illuminates between the ignition circuit terminal 86 and ground.
  5. ⇒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 breaker/fuse is open, test or replace the A/C compressor clutch relay.
  6. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
  7. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  8. Disconnect the harness connector at the A/C compressor clutch.
  9. Test for less than 1.0 ohm between the A/C compressor clutch ground circuit terminal A and ground.
  10. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  11. Connect the harness connector at the A/C compressor clutch.
  12. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the A/C compressor clutch is activated.
  13. ⇒If the A/C compressor clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the A/C compressor.
  14. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
  15. 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.
  16. ⇒If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM/PCM.
    ⇒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/PCM.
  17. If all circuits test normal, test or replace the A/C compressor clutch relay.

Component Testing

Relay Test

  1. Ignition OFF, disconnect the A/C compressor clutch relay.
  2. Test for 60-180 ohms between terminals 85 and 86.
  3. ⇒If the resistance is not within the specified range, replace the relay.
  4. Test for infinite resistance between the following terminals:
  5. • 30 and 86
    • 30 and 87
    • 30 and 85
    • 85 and 87
    ⇒If not the specified value, replace the relay.
  6. 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 between terminals 30 and 87.
  7. ⇒If greater than the specified range, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    â€¢  Relay Replacement
    â€¢  Compressor Clutch Plate/Hub Assembly Replacement
    â€¢  Air Conditioning (A/C) High Pressure Switch Replacement
    â€¢  Air Conditioning Cycling Switch Replacement
    â€¢  Control Module References for ECM/PCM replacement, setup, and programming