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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 79 (HVAC - Manual) >> Diagnostic Information and Procedures >> Air Conditioning Compressor Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.

A/C Request Malfunction

  1. Ignition OFF and all vehicle systems OFF, disconnect the X3 harness connector at the HVAC control assembly. It may take up to 2 min for all vehicle systems to power down.
  2. Test for less than 10 Ω between the ground circuit terminal C and ground.
    • If 10 Ω or greater 
    1. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 Ω 
  3. Connect the X3 harness connector and disconnect the X2 harness connector at the HVAC control assembly, ignition ON.
  4. Verify a test lamp illuminates between the ignition circuit terminal E 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 2 Ω in the B+ circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, 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, replace the HVAC control assembly.
    • Go to next step: If the test lamp illuminates 
  5. Ignition OFF, connect the X2 harness connector at the HVAC control assembly and disconnect the X4 harness connector at the HVAC control assembly, ignition ON.
  6. Verify a test lamp illuminates between the signal circuit terminal 2 and ground with the mode switch in only the following positions:
    • MAX A/C
    • A/C
    • Bi- Level
    • Defrost
    • Blend
    • If the test lamp does not illuminate in only the specified mode switch positions 
    1. Ignition OFF, disconnect the X2 harness connector at the HVAC control assembly, ignition ON.
    2. Test for less than 1 V between the HVAC control assembly signal circuit terminal 2 X2 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for infinite resistance between the signal circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    4. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω replace the HVAC control assembly.
    • Go to next step: If the test lamp illuminates in only the specified mode switch positions 
  7. Ignition OFF, connect the X4 harness connector at the HVAC control assembly and disconnect the harness connector at the A/C low pressure switch.
  8. Connect a test lamp between terminal A and B+, ignition ON.
  9. Verify a test lamp turns ON and OFF when rotating the mode switch between MAX A/C and HEAT positions.
    • If the test lamp does not turn ON and OFF 
    1. Ignition OFF, disconnect the X4 harness connector at the HVAC control assembly, ignition ON.
    2. Test for less than 1 V between the signal circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for infinite resistance between the signal circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    4. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω replace the HVAC control assembly.
    • Go to next step: If the test lamp turns ON and OFF 
  10. Install a 3 A fused jumper wire between the signal circuit terminal B and the signal circuit terminal A.
  11. Verify the scan tool ECM A/C Request Signal parameter changes to Yes.
    • If the parameter does not change to Yes 
    1. Ignition OFF, remove the jumper wire and disconnect the X7 harness connector at the body control module, ignition ON.
    2. Test for less than 1 V between the body module control module signal circuit terminal 24 X7 and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Test for infinite resistance between the signal circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    4. Test for less than 2 Ω in the signal circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω replace the body control module.
    • Go to next step: If the parameter changes to Yes 
    12. NOTE:

    Verify the vehicle has the correct refrigerant charge before replacing the A/C low pressure switch.

  12. Test or replace the A/C low pressure switch.

A/C Compressor Malfunction

  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.
    • Go to next step: If the test lamp illuminates 
  3. Verify a test lamp illuminates between the ignition circuit terminal 86 and ground.
    • Go to next step: If the test lamp illuminates 
  4. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
  5. 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 1 V between the control circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • Go to next step: If less than 1 V
    3. Ignition OFF.
    4. Test for less than 2 Ω in the control circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, 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.
    • Go to next step: If the test lamp turns ON and OFF 
  6. 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.

    • Go to next step: If the test lamp does not illuminate 
  7. 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.
  8. Test for less than 10 Ω between the ground circuit terminal A/2 and ground.
    • If 10 Ω or greater 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 Ω 
  9. Connect the harness connector at the Q2 A/C Compressor Clutch.
  10. Ignition ON, connect a 10 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
  11. Verify the Q2 A/C Compressor Clutch is engaged.
    • If the Q2 A/C Compressor Clutch does not engage 
    1. Ignition OFF, remove the jumper wire and disconnect the harness connector at the Q2 A/C Compressor Clutch.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the control circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the Q2 A/C Compressor Clutch.
    • Go to next step: If the Q2 A/C Compressor Clutch is engaged 
  12. Test or replace the KR29 A/C Compressor Clutch Relay.
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