C-10, A/C Clutch Control Circuit Diagnosis - 3.8L

PCM delays A/C compressor clutch engagement about .4 seconds after A/C is turned on. This delay allows Idle Air Control (IAC) motor to adjust engine RPM before compressor clutch engages. PCM also disengages A/C compressor clutch during Wide Open Throttle (WOT) operation. A/C compressor clutch is energized when PCM grounds circuit No. 459. PCM may engage A/C compressor clutch during engine cranking.

1. A/C compressor clutch should not be engaged with engine running if an A/C mode is not selected at control head.
2. A/C compressor clutch should apply if conditions under NOTICE at top of chart are met.
3. Checks for an A/C request signal from control head to pressure cycling switch.
   Fig 1: A/C Clutch Circuit Schematic (3.8L)

   Courtesy of GENERAL MOTORS CORP.
   Fig 2: A/C Clutch System Flow Chart (3.8L) (1 Of 3)

   Courtesy of GENERAL MOTORS CORP.
4. Checks for ignition voltage on circuit No. 639 and PCM control of ground circuit No. 459 to A/C compressor clutch relay coil.
5. Checks for ignition voltage on circuit No. 639 to A/C compressor clutch relay contacts.
6. Determines if A/C compressor clutch relay, compressor clutch coil or circuitry is faulty.
   Fig 3: A/C Clutch Circuit Schematic (3.8L)

   Courtesy of GENERAL MOTORS CORP.
   Fig 4: A/C Clutch System Flow Chart (3.8L) (2 Of 3)

   Courtesy of GENERAL MOTORS CORP.
7. Determines if PCM is turning on A/C compressor clutch relay due to a false A/C request signal.
8. Checks for circuit No. 59 shorted to B+ or a faulty A/C compressor clutch.
9. Isolates problem to A/C control head and circuits No. 66 and 257 to pressure cycling switch or circuit No. 67 and PCM.
10. Determines if A/C compressor clutch relay is faulty or A/C compressor clutch relay control circuit No. 459 is grounded at all times.
    Fig 5: A/C Clutch Circuit Schematic (3.8L)

    Courtesy of GENERAL MOTORS CORP.
    Fig 6: A/C Clutch System Flow Chart (3.8L) (3 Of 3)

    Courtesy of GENERAL MOTORS CORP.