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Heater Performance Test (Auxiliary System)

WARNING: This page is about a different car, the 2002 GMC Safari and 2002 Chevrolet Astro. 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: Definition: Rear heating system performance.
  1. Were you sent here from TOO COLD IN VEHICLE? If so, go to next step. If not, see TOO COLD IN VEHICLE  under SYMPTOM TESTS.
  2. Start the engine. Allow the engine to idle. Does the engine reach a 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 coolant 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 coolant 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 coolant bypass valve. See COOLANT BYPASS VALVE  under REMOVAL & INSTALLATION. Inspect the coolant bypass valve for the following conditions: Binding, restrictions or damage. Replace valve as necessary. 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 auxiliary HVAC module case and auxiliary air ducts for cold air leaks. Perform any necessary repairs. After necessary repairs are completed, 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 ignition off. Back-flush the auxiliary heater core. Start the engine and 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 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 HEATER CORE (AUXILIARY)  under REMOVAL & INSTALLATION. After repairs are completed, go to step  16.
  12. Replace auxiliary coolant bypass valve. See COOLANT BYPASS VALVE  under REMOVAL & INSTALLATION. After repairs are completed, go to step  16.
  13. Repair the vacuum condition. See VACUUM DIAGRAMS . After repairs are completed, go to step  16.
  14. Repair the low engine temperature concern. After repairs are completed, go to step  16.
  15. Inspect the auxiliary heater case for proper air flow. Repair as needed. After repairs, go to next step.
  16. Operate the system in order to verify the repair. Did you find and correct the condition? If so, system is okay. If not, go to step  2.
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