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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 986 (HVAC System - Automatic) >> Diagnostic Information and Procedures >> Air Conditioning Compressor Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  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.
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