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Vacuum System Diagnostics

WARNING: This page is about a different car, the 2002 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Start engine. Turn blower motor fan to ON position and select an air outlet mode. If air flows out of selected HVAC outlet ducts, go to step  19. If air does not flow out of selected HVAC outlet ducts, go to next step.
  2. If air flows out of correct ducts at first, but then changes during higher engine RPM, go to step  11. If air does not flow out of correct ducts at first, and then changes during higher engine RPM, go to next step.
  3. Cycle HVAC controls through all modes. If air flows out of selected outlet ducts now, go to step  19. If air does not flow out of selected ducts, go to next step.
  4. Start engine. Take a vacuum reading at manifold vacuum port that supplies vacuum to HVAC control solenoid. If engine vacuum is present, go to next step. If engine vacuum is not present, go to step  18.
  5. Take a vacuum reading at the vacuum supply line at the HVAC control solenoid. If vacuum reading is the same as engine vacuum, go to next step. If vacuum reading is not the same as engine vacuum, go to step  9.
  6. Take a vacuum reading at output side of HVAC control solenoid, for non-functioning mode setting. See VACUUM DIAGRAMS  to determine correct actuator operation. If vacuum is present at output side of HVAC control solenoid, go to next step. If vacuum is not present at output side of HVAC control solenoid, go to step  14.
  7. Disconnect actuator vacuum line and apply vacuum to actuator. If actuator retracts, go to step  9. If actuator does not retract, go to next step.
  8. With actuator disconnected, inspect door for binding. If door moves freely, go to step  10. If door does not move freely, go to step  16.
  9. Inspect for leaking or collapsed vacuum lines. If vacuum lines are leaking, go to step  17. If vacuum lines are not leaking, go to step  13.
  10. Replace appropriate vacuum actuator. See ACTUATORS  under REMOVAL & INSTALLATION. After repairs are complete, go to step  19.
  11. With vacuum gauge connected to actuator vacuum line, 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  9.
  12. Disconnect vacuum line from HVAC control solenoid. With vacuum gauge connected, re-start 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  14.
  13. Replace vacuum reservoir tank. See VACUUM TANK  under REMOVAL & INSTALLATION. After repairs are complete, go to step  19.
  14. Test operation of HVAC vacuum control solenoid. See TEST A: AIR DELIVERY IMPROPER  under SYMPTOM TESTS. If control solenoid operates properly, go to step  19. If control solenoid does not operate properly, go to next step.
  15. Replace HVAC vacuum control solenoid. See VACUUM CONTROL ASSEMBLY  under REMOVAL & INSTALLATION. After repairs are complete, go to step  19.
  16. Repair binding door. See AIR DISTRIBUTION DOORS  under REMOVAL & INSTALLATION. After repair is complete, go to step  19.
  17. Repair or replace collapsed or leaking vacuum line. After repair or replacement, go to step  19.
  18. Repair no vacuum condition. After repair is complete, go to next step.
  19. Cycle HVAC controls through all modes to verify proper operation. If system does not operate properly, go to step  1. Is system operates correctly, test is complete.
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