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Home >> Buick >> 2015 >> Regal GS, AWD >> Repair and Diagnosis >> Heating, Ventilation & A/C (HVAC) >> HVAC Control Systems >> HVAC System - Automatic >> Diagnostic Information and Procedures >> DTC P0645, P0646, or P0647: Air Conditioning (A/C) Compressor Clutch Relay >> Circuit/System Testing

Circuit/System Testing

  1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF, remove the test lamp.
    2. Test for less than 2Ω in the B+ circuit end to end.
      • If 2Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2Ω, verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition OFF, remove the test lamp.
    2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance
    3. Disconnect the harness connector at the Q2 A/C Compressor Clutch.
    4. Test for infinite resistance between the control circuit terminal 87 and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, test or replace the Q2 A/C Compressor Clutch.
    • If the test lamp illuminates 
  3. Ignition ON.
  4. Verify a test lamp illuminates between the ignition circuit terminal 86 and ground.
    • If the test lamp illuminates 
  5. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
  6. Verify the test lamp turns ON and OFF when commanding the ECM A/C Compressor Clutch Relay On and Off with a scan tool.
    • If the test lamp is always OFF 
    1. Ignition OFF, remove the test lamp and disconnect the harness connector at the K20 Engine Control Module, ignition ON.
    2. Test for less than 1V between the control circuit and ground.
      • If 1V or greater, repair the short to voltage on the circuit.
      • If less than 1V
    3. Ignition OFF.
    4. Test for less than 2Ω in the control circuit end to end.
      • If 2Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2Ω, replace the K20 Engine Control Module.
    • If the test lamp is always ON 
    1. Ignition OFF, remove the test lamp and disconnect the harness connector at the K20 Engine Control Module.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the K20 Engine Control Module.
    • If the test lamp turns ON and OFF 
  7. Verify a test lamp does not illuminate between the control circuit terminal 87 and ground.
    • If the test lamp illuminates 

      Repair the short to voltage on the circuit.

    • If the test lamp does not illuminate 
  8. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the Q2 A/C Compressor Clutch. It may take up to 2 min for all vehicle systems to power down.
  9. Test for less than 10Ω between the ground circuit terminal 1 and ground.
    • If 10Ω or greater 
    1. Ignition OFF.
    2. Test for less than 2Ω in the ground circuit end to end.
      • If 2Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2Ω, repair the open/high resistance in the ground connection.
    • If less than 10Ω 
  10. Connect the harness connector at the Q2 A/C Compressor Clutch.
  11. Ignition ON, connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
  12. Verify the Q2 A/C Compressor Clutch is engaged.
    • If the Q2A/C Compressor Clutch does not engage 
    1. Ignition OFF, disconnect the harness connector at the Q2 A/C Compressor Clutch.
    2. Test for less than 2Ω in the control circuit end to end.
      • If 2Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2Ω, test or replace the Q2 A/C Compressor Clutch.
    • If the Q2A/C Compressor Clutch is engaged 
  13. Test or replace the KR29 A/C Compressor Clutch Relay.
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