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CIRCUIT DESCRIPTION:

The A/C clutch control relay is controlled by the ECM to delay clutch engagement for approximately 0.4 seconds after the A/C system is powered. This allows the ECM to adjust engine speed before the A/C clutch engages. The ECM also disengages the A/C clutch during Wide Open Throttle (WOT) operation.

When the A/C selector control is switched to the "ON" position, ignition voltage is supplied to the pressure cycling switch. If there is sufficient A/C charge, the pressure cycling switch will be closed to complete the circuit to the ECM and A/C clutch control relay.

When the A/C request signal is received by the ECM, the ECM will ground relay circuit 459 long enough to adjust the engine idle speed. Once the idle speed has been adjusted, the ECM will remove the ground from the relay circuit 459. This will allow current to flow through the relay and to the A/C compressor clutch.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. This checks to see if the ECM is controlling the A/C clutch relay.

2. Checks for clutch relay feed circuits shorted to voltage.

3. This confirms a 12 volt supply to the A/C clutch relay.

4. Before replacing C-68 A/C components, refer to Locations.


DIAGNOSTIC AIDS:

^ The ECM will disengage the A/C clutch whenever a power steering load or wide open throttle is detected.