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Vacuum Control System Diagnostics

WARNING: This page is about a different car, the 2002 Pontiac Sunfire and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
  1. Start engine. Turn blower on and select an air outlet mode. If air flows out selected air outlets, go to step  3. If air does not flow out selected air outlets, go to next step.
  2. If air flows out the correct outlets at first, but then changes during higher engine speed, go to step  7. If air flows out the correct outlets at first, and does not change during higher engine speed, go to next step.
  3. With engine running, 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. With engine running, take a vacuum reading at the manifold vacuum port that supplies vacuum to HVAC vacuum control assembly. If there is full engine vacuum, go to step  6. If there is not full engine vacuum, go to next step.
  5. Repair the no vacuum condition. If repair is complete, go to step  18.
  6. Take a vacuum reading at the vacuum supply line at HVAC vacuum control assembly. If vacuum reading is same as the engine vacuum, go to step  11. If vacuum reading is not same as the engine vacuum, go to step  8.
  7. Disconnect vacuum supply line from HVAC vacuum control assembly. With vacuum gage connected to vacuum supply line, re-start engine and turn engine off. If system loses vacuum after turning off engine, go to next step. If system does not lose vacuum after turning off engine, go to step  11.
  8. Check for leaking or collapsed vacuum lines between engine manifold vacuum port and HVAC vacuum control assembly. If vacuum lines are leaking or collapsed, go to next step. If vacuum lines are not leaking or collapsed, go to step  10.
  9. Repair or replace the collapsed or leaking vacuum line. If repair is complete, go to step  18.
  10. Replace vacuum tank. See HVAC MODULE  under REMOVAL & INSTALLATION. After repairs are complete, go to step  18.
  11. Using an external vacuum source, apply vacuum to the appropriate vacuum line at connector to HVAC vacuum control assembly. See VACUUM DIAGRAMS . If actuator retracts, go to step  17. If actuator does not retract, go to next step.
  12. Check for leaking or collapsed vacuum lines between actuator and connector to HVAC vacuum control assembly. If vacuum lines are leaking, go to step  9. If vacuum lines are not leaking, go to next step.
  13. Disconnect vacuum line from actuator. Apply an external vacuum source to the actuator. If actuator retracts, go to next step. If actuator does not retract, go to step  16.
  14. With actuator 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 the binding actuator door. See VACUUM ACTUATORS & ACTUATOR DOORS  under REMOVAL & INSTALLATION. If repair is complete, go to step  18.
  16. Replace vacuum actuator. See VACUUM ACTUATORS & ACTUATOR DOORS  under REMOVAL & INSTALLATION. After repairs are complete, go to step  18.
  17. Replace HVAC control assembly. See HVAC CONTROL ASSEMBLY  under REMOVAL & INSTALLATION. If replacement is complete, go to next step.
  18. Cycle HVAC controls through all modes to verify proper operation. If the condition has been corrected, system is okay.
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