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Vacuum Control System

  1. Were you sent here from SYMPTOM DIAGNOSIS  or another diagnostic table? If so, go to next step. If not, see SYMPTOM DIAGNOSIS  under TROUBLE SHOOTING.
  2. Start engine. Turn blower motor fan on, and select an air outlet mode. If air flows out of selected HVAC outlet ducts, go to step  4. If air does not flow out of selected HVAC outlet ducts, go to next step.
  3. If air flows out correct duct initially, then changes during higher RPM, go to step  8. If air flows out incorrect duct, go to next step.
  4. With engine running, cycle HVAC controls through all modes. If air flows out of selected outlet ducts, go to step  19. If air does not flow out of selected outlet duct, go to next step.
  5. With engine running, take a vacuum reading at manifold vacuum port that supplies vacuum to HVAC vacuum control assembly. If engine vacuum exists, go to step  7. If engine vacuum does not exist, go to next step.
  6. Repair no vacuum condition. After repair is complete, go to step  19.
  7. Take a vacuum reading at vacuum supply line from HVAC vacuum control assembly. If vacuum reading is equal to engine vacuum reading, go to step  12. If vacuum reading is not equal to engine vacuum reading, go to step  9.
  8. Disconnect vacuum supply line from HVAC vacuum control assembly. With vacuum gauge connected to vacuum supply line, restart engine and turn engine off. If system loses vacuum after turning engine off, go to next step. If system does not lose vacuum after turning engine off, go to step  12.
  9. Inspect for leaking or collapsed vacuum lines or check valve between engine manifold vacuum port and HVAC vacuum control assembly. If lines are leaking, go to next step. If lines are not leaking, go to step  11.
  10. Repair or replace collapsed or leaking vacuum line. After repair is complete, go to step  19.
  11. Replace vacuum storage tank. See VACUUM STORAGE TANK  under REMOVAL & INSTALLATION. After replacement, go to step  19.
  12. Using an external vacuum source, apply vacuum to appropriate vacuum line at connector to HVAC vacuum control assembly. If actuator retracts, go to step  18. If actuator does not retract, go to next step.
  13. Inspect for leaking or collapsed vacuum lines between actuator and connector to HVAC vacuum control assembly. If vacuum lines are leaking, go to step  10. If vacuum lines are not leaking, go to next step.
  14. Disconnect vacuum line from actuator. Apply an external vacuum source to actuator. If actuator retracts, go to next step. If actuator does not retract, go to step  17.
  15. With actuator disconnected, inspect door for binding. If door moves freely, go to step  17. If door does not move freely, go to next step.
  16. Repair appropriate binding door. See REMOVAL & INSTALLATION . After replacement, go to step  19.
  17. Replace appropriate vacuum actuator. See TEMPERATURE DOOR ACTUATOR  under REMOVAL & INSTALLATION. After replacement, go to step  19.
  18. Replace HVAC vacuum control assembly. See VACUUM CONTROL ASSEMBLY  under REMOVAL & INSTALLATION. After replacement, go to next step.
  19. Cycle HVAC vacuum control assembly through all modes to verify proper operation. If HVAC vacuum control assembly operates properly, system is okay. If HVAC vacuum control assembly does not operate properly, go to step  2.
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