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A/C Compressor Clutch Does Not Engage

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.
NOTE: For circuit reference, see CONNECTOR IDENTIFICATION  and/or WIRING DIAGRAMS  .
NOTE: Definition: The A/C compressor clutch will not engage when an A/C request has been made and a Powertrain DTC has not been set.
  1. Did you review DESCRIPTION & OPERATION and perform the necessary inspections? If so, go to next step. If not, see DESCRIPTION , OPERATION  and TROUBLE SHOOTING  .
  2. Install a scan tool. Start the engine. With a scan tool, observe the ECT parameter in the Powertrain data list. Does the scan tool indicate that the ECT parameter is below 250°F (121°C)? If so, go to next step. If not, check engine for overheating.
    3. NOTE: For A/C compressor operation, outside air temperature must be above 38°F (3°C).
  3. Start the engine. Place the blower motor switch in the maximum speed position. Place the mode switch in the bi-level position. Place the air temperature control switch in the coldest position. Does the A/C compressor operate? If so, see SYMPTOM DIAGNOSIS  under TROUBLE SHOOTING. If not, go to next step.
  4. Park the vehicle inside or in the shade. Open the windows in order to ventilate the interior of the vehicle. If the A/C system was operating, allow the A/C system to equalize for approximately 2 minutes. Ensure that the ignition key is in the OFF position. Install the ACR 2000 Air Conditioning Service Center. Record the outside air temperature at the vehicle. Record readings of the low and high side static pressures. Compare the pressure values with the specifications for the ambient air temperature. Are the pressure values within specifications for the ambient air temperature, and within 15 psi (103 kPa) of each other? If so, go to next step. If not, Check for refrigerant leak. See LEAK TESTING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING.
  5. Is the HVAC control assembly inoperative? If so, go to step  19. If not, go to next step.
  6. Start the engine. With a scan tool, observe the A/C request parameter. Place the air temperature switch in the coldest position. Place the mode switch in the bi-level position. Does the scan tool indicate that the A/C request parameter is YES? If so, go to step  8. If not, go to next step.
  7. Turn ignition off. Disconnect the A/C high pressure switch. Connect a 3 amp fused jumper wire between the A/C request circuits at the A/C high pressure switch connector. Start the engine. With a scan tool, observe the A/C request parameter. Place the air temperature switch in the coldest position. Place the mode switch in the bi-level position. Does the scan tool indicate that the A/C request parameter is YES? If so, go to step  31. If not, go to step  25.
  8. Observe A/C compressor cycling in the Engine Data 2 data list. Does the scan tool indicate the A/C compressor cycling parameter is normal? If so, go to step  10. If not, go to next step.
  9. Turn ignition off. Disconnect the A/C low pressure switch. Connect a 3 amp fused jumper wire between the A/C low pressure switch signal and ground circuits. Start the engine. With a scan tool, observe the A/C compressor cycling parameter in the Engine Data 2 data list. Does the scan tool indicate the A/C compressor cycling parameter is normal? If so, go to step  28. If not, go to step  21.
  10. With a scan tool, command the A/C compressor clutch relay ON and OFF. Does the A/C compressor clutch relay turn ON and OFF with each command? If so, go to step  16. If not, go to next step.
  11. Turn ignition off. Disconnect the A/C compressor clutch relay. Turn ignition on. Probe the coil side voltage supply circuit of the A/C compressor clutch relay with a test light that is connected to a good ground. Does the test light illuminate? If so, go to next step. If not, go to step  26.
  12. Connect a test light between the control circuit of the A/C compressor clutch relay and the coil side voltage supply circuit of the A/C compressor clutch relay. With a scan tool, command the A/C compressor clutch relay ON and OFF. Does the test light turn ON and OFF with each command? If so, go to step  27. If not, go to next step.
  13. Does the test light remain illuminated with each command? If so, go to step  15. If not, go to next step.
  14. Check the control circuit of the A/C compressor clutch relay for an open. See WIRING DIAGRAMS . Did you find and correct the condition? If so, go to step  39. If not, go to next step.
  15. Check the control circuit of the A/C compressor clutch relay for a short to ground. See WIRING DIAGRAMS . Did you find and correct the condition? If so, go to step  39. If not, go to next step.
  16. Turn ignition off. Disconnect the A/C compressor clutch relay. Probe the switch side voltage supply circuit of the A/C compressor clutch relay with a test light that is connected to a good ground. Does the test light illuminate? If so, go to next step. If not, go to step  18.
  17. Connect a 10-amp fused jumper wire between the switch side voltage circuit of the A/C compressor clutch relay and the A/C compressor clutch supply voltage circuit of the A/C compressor clutch. Turn ignition on. Does the A/C compressor clutch engage? If so, go to step  27. If not, go to step  23.
  18. Repair the switch side voltage supply circuit of the A/C compressor clutch relay. See WIRING DIAGRAMS . After repairs are complete, go to step  39.
  19. Check the ignition voltage circuit of the HVAC control assembly for a short to ground, a high resistance, or an open. See WIRING DIAGRAMS . After repairs are complete, go to step  39.
  20. Check the ground circuit of the HVAC control assembly for an open. See WIRING DIAGRAMS . Did you find and correct the condition? If so, go to step  39. If not, go to step  30.
  21. Check the A/C low pressure switch signal circuit for a high resistance or an open. See WIRING DIAGRAMS . Did you find and correct the condition? If so, go to step  39. If not, go to next step.
  22. Check the ground circuit of the A/C low pressure switch for a high resistance or an open. See WIRING DIAGRAMS . Did you find and correct the condition? If so, go to step  39. If not, go to step  32.
  23. Check the A/C compressor clutch supply voltage circuit at the A/C compressor clutch for a short to ground, a high resistance, or an open. See WIRING DIAGRAMS . Did you find and correct the condition? If so, go to step  39. If not, go to next step.
  24. Check the ground circuit of the A/C compressor clutch for a high resistance or an open. See WIRING DIAGRAMS . Did you find and correct the condition? If so, go to step  39. If not, go to step  29.
  25. Turn ignition off. Reconnect the A/C high pressure switch. Check the A/C request signal circuit for a short to ground, a high resistance, or an open. See WIRING DIAGRAMS . Did you find and correct the condition? If so, go to step  39. If not, go to step  32.
  26. Repair the coil side voltage supply circuit of the A/C compressor clutch relay. See WIRING DIAGRAMS . After repairs are complete, go to step  39.
  27. Inspect for poor connections at the A/C compressor clutch relay. Did you find and correct the condition? If so, go to step  39. If not, go to step  33.
  28. Inspect for poor connections at the harness connector of the A/C low pressure switch. Did you find and correct the condition? If so, go to step  39. If not, go to step  34.
  29. Inspect for poor connections at the harness connector of the A/C compressor clutch. Did you find and correct the condition? If so, go to step  39. If not, go to step  36.
  30. Inspect for poor connections at the harness connector of the HVAC control assembly. Did you find and correct the condition? If so, go to step  39. If not, go to step  37.
  31. Inspect for poor connections at the harness connector of the A/C high pressure switch. Did you find and correct the condition? If so, go to step  39. If not, go to step  35.
  32. Inspect for poor connections at the harness connector of the PCM. See WIRING DIAGRAMS . Did you find and correct the condition? If so, go to step  39. If not, go to step  38.
  33. Replace the A/C compressor clutch relay. After repairs are complete, go to step  39.
  34. Replace the A/C low pressure switch. After repairs are complete, go to step  39.
  35. Replace the A/C high pressure switch. After repairs are complete, go to step  39.
  36. Replace the A/C compressor clutch coil. See COMPRESSOR SERVICING in GENERAL SERVICING PROCEDURES article in GENERAL SERVICING. After repairs are complete, go to step  39.
  37. Replace the HVAC control assembly. After repairs are complete, go to step  39.
  38. Replace the PCM. See REMOVAL, OVERHAUL & INSTALLATION - ASTRO & SAFARI article. After repairs, perform the reprogramming procedure for the PCM. After repairs, go to next step.
  39. Operate the system in order to verify the repair. Did you correct the condition? If so, repairs are complete. If not, go to step  1.
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