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Heater Performance Test (Auxiliary System)

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.
WARNING: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury.
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.
NOTE: Definition: Rear heating system performance.
  1. Did you review the DESCRIPTION  and OPERATION  ? If so, go to next step. If not, see DESCRIPTION  and OPERATION  , then go to next step.
  2. Start the engine. Allow the engine to idle. Does the engine reach normal operating temperature? If so, go to next step. If not, go to step  14.
  3. Allow the engine to idle. Select the maximum auxiliary temperature setting. Select the minimum auxiliary blower speed. Feel the temperature of the inlet and outlet hoses to the auxiliary hot water bypass valve. Does the inlet hose feel warmer than the outlet hose? If so, go to next step. If not, go to step  6.
  4. Disconnect the vacuum hose from the auxiliary hot water bypass valve. Is vacuum being applied to the valve? If so, go to step  13. If not, go to next step.
  5. Remove the auxiliary hot water bypass valve. See AUXILIARY HOT WATER BY-PASS VALVE  under REMOVAL & INSTALLATION. Inspect the hot water bypass valve for binding, restrictions or damage. After repairs are complete, go to step  16.
  6. Allow the engine to idle. Select the minimum auxiliary blower speed. Select the maximum auxiliary temperature setting. Feel the temperature of the inlet and outlet hoses to the auxiliary heater core. Does the inlet hose feel warmer than the outlet hose? If so, go to step  10. If not, go to next step.
  7. Install a thermometer into an auxiliary air outlet. Secure a thermometer on the outlet hose of the auxiliary heater core. Select the maximum auxiliary blower speed. Select the maximum auxiliary temperature setting. Record the temperature at the auxiliary air outlet and the auxiliary heater core outlet hose. Compare the recorded temperatures. Are the temperatures similar? If so, go to next step. If not, go to step  9.
  8. Inspect the following areas of the vehicle for cold air leaks:
    • The Auxiliary HVAC Module Case
    • The Auxiliary Air Ducts
    Perform any necessary repairs, then go to step  16.
  9. Inspect the auxiliary HVAC module for correct temperature door operation. See SYMPTOM DIAGNOSIS  under TROUBLE SHOOTING. Does the temperature door operate correctly? If so, go to step  16. If not, go to step  15.
  10. Turn the engine off. Backflush the auxiliary heater core. Start the engine and allow the engine to reach operating temperature. Select the minimum auxiliary blower speed. Select the maximum auxiliary temperature setting. Feel the temperature of the inlet and outlet hoses in the auxiliary heater core. Does the inlet hose feel warmer than the outlet hose? If so, go to next step. If not, go to step  16.
  11. Replace the auxiliary heater core. See AUXILIARY HEATER CORE  under REMOVAL & INSTALLATION. After repairs are complete, go to step  16.
  12. Replace auxiliary hot water bypass valve. See AUXILIARY HOT WATER BY-PASS VALVE  under REMOVAL & INSTALLATION. After repairs are complete, go to step  16.
  13. Repair the vacuum condition. After repairs are complete, go to step  16.
  14. Repair the low engine temperature concern. After repairs are complete, go to step  16.
  15. Repair the temperature door operation. See TEMPERATURE DOOR  under REMOVAL & INSTALLATION. After repairs are complete, go to step  16.
  16. Operate the system in order to verify the repair. Does the system operate correctly? If so, system is okay. If not, go to step  2.
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