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Circuit/System Testing

WARNING: This page is about a different car, the 2010 GMC Canyon and 2010 Chevrolet Colorado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the harness connector at the evaporator temperature sensor.
  2. Test for less than 5 ohms between the ground circuit terminal 3 and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Verify the scan tool A/C High Side Pressure Sensor parameter is less than 0.1 volts (1 psi).
    • If greater than the specified range, test the signal circuit terminal 3 for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Ignition OFF, connect the harness connector at the evaporator temperature sensor.
  5. Engine running, observe the scan tool BCM A/C Request parameter while cycling the A/C switch on the HVAC control module. The parameter should change between Yes and No.
    • If the parameter does not change between the specified values, test the signal circuit terminal A43 for a short to ground or an open high/resistance. If the circuit tests normal, test or replace the evaporator temperature sensor. If the A/C compressor remains inoperative, replace the BCM.
  6. Ignition OFF, disconnect the A/C relay.
  7. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 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 an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test or replace the relay.
  9. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
    • 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 is open, test the control circuit terminal for a short to ground.
  10. Disconnect the harness connector at the A/C compressor clutch.
  11. Test for less than 1.0 ohm between the ground circuit terminal B 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 compressor clutch.
  13. 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.
    • 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.
  14. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
  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.
    • 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 relay.
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