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Home >> Saturn >> 2007 >> Relay 3.9 1 >> Repair and Diagnosis >> External Pages >> Different car >> Section 39 (HVAC System - Automatic) >> Diagnostic Information and Procedures >> DTC P0645 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2007 Saturn Outlook. However, it is still accessible from the selected car via links, so may be relevant.

The A/C Compressor Clutch Relay is located in the Underhood BEC.

  1. Ignition OFF, disconnect the A/C Compressor Clutch Relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the A/C Compressor Clutch Relay control circuit terminal 87 and ground.
    • If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the ignition circuit, relay coil feed 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 the ignition circuit fuse is open, test or replace the a/c compressor clutch relay.
  4. 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, test or replace the a/c compressor clutch relay.
  5. Disconnect the harness connector at the A/C Compressor Clutch Coil.
  6. Test for less than 1 ohm of resistance between the A/C Compressor Clutch Coil ground circuit terminal 86 and ground.
    • If greater than 1 ohm, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the A/C Compressor Clutch Coil.
  8. Connect a 3-amp fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87 of the A/C Compressor Clutch Relay. Verify the A/C Compressor Clutch Relay is activated.
    • If the A/C Compressor Clutch Relay 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 Relay.
  9. Connect a test lamp between the coil side of the A/C Compressor Clutch Relay ignition circuit terminal 85 and the control circuit terminal 86.
  10. 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.
  11. If all circuits test normal, test or replace the A/C Compressor Clutch Relay.
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