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Test M: Vacuum Control System Diagnosis

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, 2002 Chevrolet RV Cutaway, and 2002 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: For circuit reference, see CONNECTOR IDENTIFICATION  and/or WIRING DIAGRAMS  .
NOTE: The manufacturer does not separate testing by "heater only" or "air conditioned" vehicles. References to air conditioning operations or repairs may not apply to vehicles without air conditioning. References to some components also may not apply to vehicles without air conditioning.
  1. Start the engine. Turn the blower motor fan on and select an air outlet mode. Does air flow out of the selected HVAC outlet ducts? If so, go to step  3. If not, go to next step.
  2. Did the customer concern mention that the air discharges out the correct ducts at first, but then changes during higher engine RPM? If so, go to step  7. If not, go to next step.
  3. With the engine running, cycle the HVAC controls through all the modes. Does the air come out of the selected outlet ducts? If so, go to step  18. If not, go to next step.
  4. With the engine running, take a vacuum reading at the manifold vacuum port that supplies vacuum to the HVAC vacuum control assembly. Is there engine vacuum? If so, go to step  6. If not, go to next step.
  5. Repair the no vacuum condition. After repairs are complete, go to step  18.
  6. Take a vacuum reading at the vacuum supply line at the HVAC vacuum control assembly. Is the vacuum reading the same as the engine vacuum? If so, go to step  11. If not, go to step  8.
  7. Disconnect the vacuum supply line from the HVAC vacuum control assembly. With the vacuum gauge connected to the vacuum supply line, restart the engine and turn the engine Off. Does the system lose vacuum after turning the engine Off? If so, go to next step. If not, go to step  11.
  8. Inspect for leaking or collapsed vacuum lines between the engine manifold vacuum port and the HVAC vacuum control assembly. Are the vacuum lines leaking? If so, go to next step. If not, go to step  10.
  9. Repair or replace the collapsed or leaking vacuum line. After repairs are complete, go to step  18.
  10. Replace the vacuum reservoir tank. See VACUUM RESERVOIR TANK  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 the connector to the HVAC vacuum control assembly. See VACUUM DIAGRAMS . Does the actuator retract? If so, go to step  17. If not, go to next step.
  12. Inspect for leaking or collapsed vacuum lines between the actuator and the connector to the HVAC vacuum control assembly. Are the vacuum lines leaking? If so, go to step  9. If not, go to next step.
  13. Disconnect the vacuum line from the actuator. Apply an external vacuum source to the actuator. Did the actuator retract? If so, go to next step. If not, go to step  16.
  14. With the actuator disconnected, inspect the door for binding. Does the door move freely? If so, go to step  16. If not, go to next step.
  15. Repair the appropriate binding door. See REMOVAL & INSTALLATION . After repairs are complete, go to step  18.
  16. Replace the appropriate vacuum actuator. See REMOVAL & INSTALLATION . After repairs are complete, go to step  18.
  17. Replace the HVAC control assembly. See HVAC CONTROL ASSEMBLY . After repairs are complete, go to next step.
  18. Cycle the HVAC controls through all modes to verify proper operation. Did you correct the condition? If so, system is okay. If not, go to step  1.
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