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Test I: Defrosting Insufficient

NOTE: For circuit reference, see CONNECTOR IDENTIFICATION  and/or WIRING DIAGRAMS  .
  1. Start the engine. Select the DEFROST mode. Select the maximum blower speed. Does sufficient air flow from the defroster outlets? If so, go to next step. If not, go to step  9.
  2. Measure the engine operating temperature. Does engine reach a normal operating temperature? If so, go to next step. If not, go to step  4.
  3. Select the minimum blower speed. Select the maximum temperature setting. Feel the temperature of the inlet and outlet hoses at the heater core. Does the inlet hose feel warmer than the outlet hose? If so, go to step  5. If not, go to step  11.
  4. Repair the low engine temperature concern. After repairs are complete, go to step  13.
  5. Check the operation of the A/C compressor clutch. Does the A/C compressor clutch engage? If so, go to step  7. If not, go to next step.
  6. Repair the A/C compressor clutch. See COMPRESSOR SERVICING article in GENERAL SERVICING. After repairs are complete, go to step  13.
  7. Perform the A/C system performance test. See A/C PERFORMANCE TEST  in PERFORMANCE TESTS. Is the A/C system operating within the specifications? If so, go to next step. If not, go to step  10.
  8. Inspect for correct operation of the recirculation door. Is the recirculation door operating correctly? If so, go to step  13. If not, go to step  12.
  9. Repair the air delivery concern. See TEST D: AIR DELIVERY IMPROPER . After repairs are complete, go to step  13.
  10. Repair the A/C performance concern. After repairs are complete, go to step  13.
  11. Repair the heating concern. See HEATER PERFORMANCE TEST  in PERFORMANCE TESTS. After repairs are complete, go to step  13.
  12. Repair the recirculation door concern. See RECIRCULATION DOOR under REMOVAL & INSTALLATION in SONOMA & S10 PICKUP article in HEATER SYSTEMS. After repairs are complete, go to step  13.
  13. Operate the system in order to verify the repair. Does the system operate correctly? If so, system okay. If not, go to step  1.
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