Chart C10 - A/C Clutch Control: Notes

The ECM control of the A/C clutch improves idle quality and performance by the following conditions:

• Delaying clutch application until idle air rate is increased.
• Releasing clutch when idle speed is too low or during high power steering loads.
• Releasing clutch at Wide Open Throttle (WOT).
• Smooths cycling of the compressor by providing additional fuel at the instant clutch is applied.

Voltage is supplied to the A/C clutch control relay on circuit No. 50 when the A/C power relay is energized by the A/C control switch. Also, when the A/C is turned on, voltage is supplied to the A/C relay coil on circuit No. 67 through the closed pressure cycling switch. This same voltage is supplied as a signal to ECM pin "B8". After a time delay of about a 1/2 second the ECM will ground terminal "C2" (circuit No. 459) and close the A/C relay contacts. When the relay is energized by battery voltage from circuit No. 50, a signal is sent to the A/C clutch through the A/C clutch relay and circuit No. 59.

1. The ECM will only energize the A/C relay when the engine is running. This test will determine if the relay or circuit No. 459 is faulty.
2. In order for the clutch to be properly engaged, the pressure cycling switch must be closed to provide 12 volts to the relay and the high pressure switch must be closed, so the A/C request (12 volts) will be present at the ECM.
3. Determines if the signal is reaching the ECM on circuit No. 66 from the A/C control panel. Signal should only be present when the A/C mode or defrost mode has been selected.
4. A short to ground in any part of the A/C request circuit could be the cause of the blown fuse.
5. With the ignition on and the diagnostic "test" terminal grounded, the ECM should be grounding circuit No. 459, which should cause the test light to be on.