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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1944 (HVAC System - Automatic) >> Diagnostic Information and Procedures >> DTC B0228, B0423, or B3779 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the harness connector at the appropriate actuator.
  2. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal 1 and ground.
    • If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 3 and ground.
    • If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
    • If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.
  4. Verify the appropriate scan tool Door Position parameter is greater than 250 counts.
    • If less than the specified range, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the HVAC control module.
  5. Install a 3A fused jumper wire between the signal circuit terminal 2 and the low reference circuit terminal 1. Verify the appropriate scan tool Door Position parameter is less than 3 counts.
    • If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  6. Ignition OFF, test for less than 10 ohms between the control circuit terminal 4 and ground.
    • If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance. If circuit tests normal, replace the HVAC control module.
  7. Ignition OFF, test for less than 10 ohms between the control circuit terminal 5 and ground.
    • If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance. If circuit tests normal, replace the HVAC control module.
  8. Connect a test lamp between control circuit terminal 5 and control circuit terminal 4.
  9. Command the appropriate actuator door in both directions with a scan tool. The test lamp should turn ON and OFF when commanded in both directions.
    • If the test lamp remains OFF during either of the commands, test for a short to ground on either control circuit. If the circuits test normal, replace the HVAC control module.
  10. If both circuits test normal, test or replace the actuator.
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