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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 >> Auxiliary Blower Motor Malfunction (RPO C69 with Rear Controls) >> Circuit/System Testing

Circuit/System Testing

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Blower Motor Inoperative - Front Control

  1. Ignition OFF, disconnect the harness connector at the front auxiliary HVAC control assembly.
  2. Ignition OFF, 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. Connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary HVAC control assembly.
  4. Front auxiliary HVAC control assembly blower switch in the LOW position, test for infinite resistance between the signal circuit terminal M and ground.
    • If less than the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
  5. Ignition OFF, connect the harness connector at the auxiliary HVAC control assembly. Disconnect the auxiliary high speed blower motor relay.
  6. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal C2 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 the relay coil ignition circuit at each of the auxiliary blower motor relays for a short to ground. If the circuits test normal, replace the appropriate relay.
  7. Verify that a test lamp illuminates between the B+ circuit terminal C1 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 relay switch B+ circuit at each of the auxiliary blower motor relays as well as the relay switch output control circuits for a short to ground.
  8. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
  9. Test for less than 5 ohms between the ground circuit terminal A and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  10. Connect the harness connector at the auxiliary blower motor.
  11. Ignition ON, connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turns ON.
    • If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor.
  12. If all circuits test normal, test or replace the front auxiliary HVAC control assembly.

Blower Motor Malfunction - Front Control

  1. Ignition OFF, disconnect the appropriate blower motor relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal A2 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 terminal C2 and ground.
    • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. Connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turn ON.
    • If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor resistor assembly.
  6. Connect a test lamp between the ignition circuit terminal C2 and the control circuit terminal A1.
  7. Cycle the front auxiliary HVAC control assembly blower motor switch between OFF and the appropriate speed position. 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 front auxiliary HVAC control assembly.
    • 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 front auxiliary HVAC control assembly.
  8. If all circuits test normal, test or replace the appropriate auxiliary blower motor relay.

Blower Motor Inoperative - Rear Control

  1. Ignition OFF, disconnect the harness connector at the auxiliary HVAC control assembly.
  2. Test for less than 5 ohms between the ground circuit terminal H and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal J and ground.
    • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Front auxiliary HVAC control assembly blower switch in the AUX position, test for less than 5 ohms between the signal circuit terminal M and ground.
    • If greater than the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
  5. Ignition OFF, connect the harness connector at the auxiliary HVAC control assembly. Disconnect the rear auxiliary HVAC control assembly.
  6. Ignition ON, front auxiliary HVAC control assembly blower switch in the AUX position, test for less than 5 ohms between the control circuit terminal F and ground.
    • If greater than the specified range, test the control circuit for an open/high resistance. If the circuit tests normal, replace the auxiliary HVAC control assembly.
  7. Ignition OFF, connect the harness connector at the rear auxiliary HVAC control assembly. Disconnect the auxiliary high speed blower motor relay.
  8. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal C2 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 the relay coil ignition circuit at each of the auxiliary blower motor relays for a short to ground. If the circuits test normal, replace the appropriate relay.
  9. Verify that a test lamp illuminates between the B+ circuit terminal C1 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 relay switch B+ circuit at each of the auxiliary blower motor relays as well as the relay switch output control circuits for a short to ground.
  10. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
  11. Test for less than 5 ohms between the ground circuit terminal A and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  12. Connect the harness connector at the auxiliary blower motor.
  13. Ignition ON, connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turns ON.
    • If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor.
  14. If all circuits test normal, test or replace the rear auxiliary HVAC control assembly.

Blower Motor Malfunction - Rear Control

  1. Ignition OFF, disconnect the appropriate blower motor relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal A2 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 terminal C2 and ground.
    • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. Connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turn ON.
    • If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor resistor assembly.
  6. Connect a test lamp between the ignition circuit terminal C2 and the control circuit terminal A1.
  7. Front auxiliary HVAC control assembly blower switch in the AUX position, cycle the rear auxiliary HVAC control assembly blower motor switch between OFF and the appropriate speed position. 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 rear auxiliary HVAC control assembly.
    • 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 rear auxiliary HVAC control assembly.
  8. If all circuits test normal, test or replace the appropriate auxiliary blower motor relay.
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