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Vacuum Control System Diagnostics

WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
  1. Start engine. Turn blower motor on and select an air outlet mode. If air flows out of selected outlets, go to step  3. If air does not flow out from the selected outlets, go to next step.
  2. If air flows out the correct outlets at first, but changes to other outlets during higher engine speed, go to step  7. If air flow does not change to other air outlets with increased engine speed, go to next step.
  3. Cycle HVAC controls through all modes. If air flows out selected outlets, go to step  18. If air does not flow out selected outlets, go to next step.
  4. Using a vacuum gauge, measure vacuum at manifold vacuum port supply for HVAC control. If full engine vacuum is present, go to step  6. If full engine vacuum is not present, go to next step.
  5. Repair no vacuum condition. If repair is complete, go to step  18.
  6. Using a vacuum gauge, measure vacuum at vacuum supply line at HVAC control assembly. See Fig 1. If vacuum supply is the same as engine vacuum reading, go to step  11. If vacuum supply is not same as engine vacuum reading, go to step  8.
  7. Turn ignition off. Disconnect vacuum supply line from HVAC control assembly. See Fig 1. Connect vacuum gauge to HVAC control vacuum supply line. Start engine, then turn engine off. If vacuum supply appears, then dissipates after turning engine off, go to next step. If vacuum supply appears, and does not dissipate after turning engine off, go to step  11.
  8. Check for leaking or collapsed vacuum lines between engine manifold vacuum port and HVAC control assembly. If vacuum lines are leaking or collapsed, go to next step. If vacuum lines are okay, go to step  10.
  9. Repair or replace collapsed or leaking vacuum line. If repair is complete, go to step  18.
  10. Replace vacuum reservoir tank in engine compartment. After repairs are complete, go to step  18.
  11. Using an external vacuum source, apply vacuum to appropriate vacuum line at HVAC control assembly connector. See Fig 1. If appropriate actuator retracts, go to step  17. If appropriate actuator does not retract, go to next step.
  12. Check for leaking or collapsed vacuum lines between actuator and appropriate connector at HVAC control assembly. If vacuum lines are leaking or collapsed, go to step  9. If vacuum lines are okay, go to next step.
  13. Disconnect vacuum line from actuator. Using an external vacuum source, apply vacuum to actuator. If actuator retracts, go to next step. If actuator does not retract, go to step  16.
  14. With vacuum line disconnected, inspect actuator door for binding. If actuator door moves freely, go to step  16. If actuator door does not move freely, go to next step.
  15. Repair appropriate binding actuator door. See ACTUATOR DOORS  under REMOVAL & INSTALLATION. If repair is complete, go to step  18.
  16. Replace appropriate vacuum actuator. See VACUUM ACTUATORS  under REMOVAL & INSTALLATION. After repairs are complete, go to step  18.
  17. Replace HVAC control assembly. See HVAC CONTROL ASSEMBLY  under REMOVAL & INSTALLATION.
  18. Cycle HVAC controls through all modes to verify proper system operation. If the condition was corrected, system is okay.
Fig 1: Identifying HVAC Vacuum Circuits
G00067639Courtesy of GENERAL MOTORS CORP.
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