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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2002 🢒 Rendezvous - FWD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 HVAC Compressor Clutch Does Not Engage

Diagnostic Instructions

Perform the Diagnostic System Check - HVAC Systems - Manual prior to using this diagnostic procedure.

Circuit/System Description

When the A/C switch is pressed, the HVAC control module applies B+ to the A/C request signal circuit. The body control module (BCM) receives this input and sends a class 2 message to the powertrain control module (PCM) for an A/C request. This input will request the PCM 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 PCM to turn on the compressor clutch:

    • Battery voltage is between 9-16 volts.
    • Engine coolant temperature (ECT) is less than 124°C (255°F).
    • Engine speed is less than 5480 RPM.
    • Engine speed is more than 600 RPM.
    • A/C high side pressure is between 2979-219 kPa (432-32 psi).
    • Throttle position is less than 100 percent.
    • PCM does not detect excessive torque load
    • PCM does not detect insufficient idle quality.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

HVAC Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification
  1. 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
  1. Ignition OFF, disconnect the harness connector at the HVAC control module.
  2. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal C1 pin B1and ground.
    3. ⇒If greater than 1.0 ohm, test the ground circuit for an open/high resistance.
  3. Ignition ON, test for B+ between the ignition 3 circuit terminal C2 pinB and ground.
    4. ⇒If less than B+, test the ignition circuit for an open/high resistance. If the BLWR fuse 25 is open, test ignition circuit for a short to ground.
  4. Install a 3-amp fused jumper wire between the signal circuit terminal C1 pin B9 and B+. With a scan tool, verify the BCM A/C Switch parameter is ON.
    5. ⇒If not the specified value, test the signal circuit for a short to ground or an open/high resistance. If circuit tests normal, replace the BCM.
  5. Reconnect the harness connector of the HVAC control module. With a scan tool, verify the BCM A/C Switch parameter cycles between On and Off with each press of the A/C switch.
    6. ⇒If the parameter does not cycle, test the signal circuit for a short to B+. If the circuit tests normal, test or replace the HVAC control module.
  6. Remove the A/C compressor clutch relay.
  7. Verify that a test lamp illuminates between the compressor clutch relay ignition circuit terminal R7 and ground.
    8. ⇒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, test or replace the A/C compressor relay.
  8. Verify that a test lamp illuminates between the B+, circuit terminal S7and ground.
    9. ⇒If the test lamp does not illuminate, test the B+, circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse (A/C CLU Fuse 2), is open, test the control circuit terminal R5 for a short to ground.
  9. Disconnect the harness connector at the A/C compressor clutch terminal A.
  10. Test for less than 1.0 ohm of resistance between the A/C compressor clutch ground circuit terminal B and ground.
    11. ⇒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 S7 and the control circuit terminal R5. 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, test or replace the A/C compressor clutch.
  13. Connect a test lamp between the ignition circuit terminal R7and the control circuit terminal S5.
  14. Command the A/C compressor clutch relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    15. ⇒If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the 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 PCM.
  15. If all circuits test normal, test or replace the A/C compressor relay.

Repair Instructions
    •  Powertrain Control Module Replacement
    •  Powertrain Control Module Programming
    •  Blower Motor Resistor Assembly Replacement
    •  HVAC Control Module Replacement
    •  Air Conditioning Compressor Replacement