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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 35 (HVAC SYSTEMS - MANUAL)SYMPTOM TESTSTEST F: COMPRESSOR CLUTCH DOES NOT ENGAGE
1999 GMC Forward Control 5.7 R, Automatic

Test F: Compressor Clutch Does Not Engage

1999 GMC Forward Control 5.7 R, AutomaticSECTION Test F: Compressor Clutch Does Not Engage
WARNING: This page is about a different car, the 2002 Buick Regal and 2002 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
  1. If diagnostic system check was not performed, go to DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTICS SYSTEM. If diagnostic system check was performed, go to next step.
  2. Install scan tool. Start engine. Using scan tool, observe ENGINE COOLANT TEMPERATURE SENSOR parameter in Powertrain data list. If scan tool indicates ENGINE COOLANT TEMPERATURE SENSOR parameter is above 255°F (124°C) for 3.1L, or 250°F (121°C) for 3.8L, check for engine overheating condition. Repair as needed. Is can tool does indicate temperatures are to high, go to next step.
    3. NOTE: Ensure ambient air temperature is above 38°F (3°C).
  3. Start engine. Place blower motor switch in maximum speed position. Place A/C request switch in ON position. Place air temperature switch in coldest position. If A/C compressor operates, inspect wiring system and connectors for poor connections. If A/C compressor does not operate, go to next step.
  4. Park vehicle inside or in the shade. Open windows to ventilate interior of vehicle. If A/C system was operating, allow A/C system to equalize for approximately 2 minutes. Turn ignition off. Install A/C manifold gauge set. Record ambient air temperature at vehicle. Record readings of low and high side STATIC pressures. Compare pressure values with specifications for ambient air temperature. See A/C SYSTEM PERFORMANCE  under PERFORMANCE TESTS. If pressure values are within 15 psi (1.05 kg/cm 2 ) of each other and within ambient air temperature specifications, go to next step. If pressure values are not as specified, leak test system. See LEAK TESTING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING.
  5. Turn ignition on. Using scan tool, observe A/C HIGH SIDE PRESSURE parameter in Powertrain Control Module engine data 2 list. Compare A/C High Side Pressure on scan tool to high side pressure value on manifold gauge set. If high side pressure value is within 15 psi (1.05 kg/cm 2 ) of each other, go to next step. If high side pressure value is not within 15 psi (1.05 kg/cm 2 ) of each other, go to step  17.
  6. If temperature controls are inoperative, go to step  17. If temperature controls are not inoperative, go to next step.
  7. Start engine. Using scan tool, observe A/C REQUEST SIGNAL parameter in Powertrain Control Module engine data 2 list. Place air temperature switch in coldest position. Place A/C request switch in ON position. Place blower switch in maximum position. If scan tool indicates A/C REQUEST SIGNAL parameter is YES, go to step  11. If scan tool does not indicate A/C REQUEST SIGNAL parameter is ON, go to next step.
  8. If A/C request indicator illuminates, go to step  10. If A/C request indicator does not illuminate, go to next step.
  9. Ensure blower motor switch is in ON position. Turn ignition on. Check blower motor off circuit for a short to voltage. See WIRING DIAGRAMS . If short to voltage is found, repair as necessary. When repair is complete, go to step  36. If short to voltage is not found, go to step  29.
  10. Check A/C request signal circuit for a short to ground. See WIRING DIAGRAMS . If short to ground is found, repair as necessary. When repair is complete, go to step  36. If short to ground is not found, go to step  30.
  11. Using scan tool, command A/C relay ON and OFF. If A/C compressor clutch relay turns ON and OFF with each command, go to step  15. If A/C compressor clutch relay does not turn ON and OFF with each command, go to next step.
  12. Turn ignition off. Disconnect A/C compressor clutch relay. Turn ignition on. Using a test light connected to ground, probe coil side battery positive voltage circuit of A/C compressor clutch relay. If test light illuminates, go to next step. If test light does not illuminate, go to step  24.
  13. Connect test light between A/C compressor clutch relay control circuit of A/C compressor clutch relay and coil side battery positive voltage supply circuit of A/C compressor clutch relay. See WIRING DIAGRAMS . Using scan tool, command A/C Relay ON and OFF. If test light turns ON and OFF with each command, go to step  25. If test light does not turn ON and OFF with each command, go to next step.
  14. If test light remains illuminated with each command, go to step  21. If test light does not remain illuminated with each command, go to step  20.
  15. Turn ignition off. Disconnect A/C compressor clutch relay. Using test light connected to ground, probe switch side battery positive voltage circuit of A/C compressor clutch relay. If test light illuminates, go to next step. If test light does not illuminate, go to step  25.
  16. Connect 10-amp fused jumper wire between switch side battery positive voltage circuit of A/C compressor clutch relay and A/C compressor clutch supply voltage circuit of the A/C compressor clutch. See WIRING DIAGRAMS . If A/C compressor clutch engages, go to step  27. If A/C compressor clutch does not engage, go to step  22.
  17. Check ignition 3 voltage circuit of HVAC control module for short to ground, high resistance, or open. See WIRING DIAGRAMS . If short to ground, high resistance or open condition is found, repair as necessary. When repair is complete, go to step  36. If short to ground, high resistance, or open condition is not found, go to step  19.
  18. Check ground circuit of A/C refrigerant pressure sensor for open. See WIRING DIAGRAMS . If open is found, repair as necessary. When repair is complete, go to step  36. If open condition is not found, go to step  26.
  19. Check ground circuit of the HVAC control module for an open. See WIRING DIAGRAMS . If open is found, repair as necessary. When repair is complete, go to step  36. If open condition is not found, go to step  29.
  20. Check A/C compressor clutch relay control circuit of A/C compressor clutch relay for an open. See WIRING DIAGRAMS . If open is found, repair as necessary. When repair is complete, go to step  36. If open condition is not found, go to step  30.
  21. Check A/C compressor clutch relay control circuit of A/C compressor clutch relay for a short to ground. See WIRING DIAGRAMS . If short to ground is found, repair as necessary. When repair is complete, go to step  36. If short to ground condition is not found, go to step  30.
  22. Check A/C compressor clutch supply voltage circuit at A/C compressor clutch for a short to ground, a high resistance, or an open. See WIRING DIAGRAMS . If short to ground high resistance, or an open is found, repair as necessary. When repair is complete, go to step  36. If short to ground high resistance, or an open condition is not found, go to next step.
  23. Check ground circuit of A/C compressor clutch for high resistance or an open. See WIRING DIAGRAMS . If short to ground high resistance, or an open is found, repair as necessary. When repair is complete, go to step  36. If short to ground, high resistance, or an open condition is not found, go to step  28.
  24. Repair switch side battery positive voltage circuit of A/C compressor clutch relay. See WIRING DIAGRAMS . When repair is complete, go to step  36.
  25. Repair coil side battery positive voltage circuit of A/C compressor clutch relay. See WIRING DIAGRAMS . When repair is complete, go to step  36.
  26. Check A/C refrigerant pressure sensor harness connector for poor connections. If poor connection is found, repair as necessary. When repair is complete, go to step  36. If poor connection is not found, go to step  31.
  27. Check A/C compressor clutch relay for poor connections. If poor connection is found, repair as necessary. When repair is complete, go to step  36. If poor connection is not found, go to step  32.
  28. Check A/C compressor clutch harness connector for poor connections. If poor connection is found, repair as necessary. When repair is complete, go to step  35. If poor connection is not found, go to step  33.
  29. Check HVAC control module harness connector for poor connections. If poor connection is found, repair as necessary. When repair is complete, go to step  36. If poor connection is not found, go to step  34.
  30. Check powertrain control module (PCM) harness connector for poor connections. If poor connection is found, repair as necessary. When repair is complete, go to step  36. If poor connection is not found, go to step  35.
  31. Replace A/C refrigerant pressure sensor. See A/C PRESSURE SENSOR  under REMOVAL & INSTALLATION. When repair is complete, go to step  36.
  32. Replace A/C compressor clutch relay. See COMPRESSOR RELAY  under REMOVAL & INSTALLATION. When repair is complete, go to step  36.
  33. Replace A/C compressor clutch. Replace compressor and clutch as an assembly. See COMPRESSOR  under REMOVAL & INSTALLATION. When repair is complete, go to step  36.
  34. Replace HVAC control module. See HVAC CONTROL MODULE  under REMOVAL & INSTALLATION. When repair is complete, go to step  36.
  35. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CENTURY, GRAND PRIX, IMPALA, MONTE CARLO & REGAL article in ENGINE PERFORMANCE. When repair is complete, go to next step.
  36. Operate system to verify repair. If condition is corrected, system is okay. If condition is not corrected, go to step  4.
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  • • The engine overheats, stalls repeatedly, or misfires under load.
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