Component Diagnostic Charts/Tests

Chart C-10:

Wiring Diagram For A/C Clutch:

CIRCUIT DESCRIPTION:

When an A/C mode is selected on the A/C control switch, ignition voltage is supplied to the compressor low pressure switch. If there is sufficient system pressure, the low pressure switch will be closed and will complete the circuit to the high pressure cut-off switch and to circuits 67 and 459. The voltage on circuit 459 to the ECM is shown on the Scan tool as "ON" (voltage present) or "OFF" (no voltage). When a request for A/C is sensed by the ECM, the ECM will ground circuit 458 of the A/C clutch control relay. The relay will then send current to circuits 459 and 59 to engage the A/C compressor clutch. A Scan tool will display circuit 458 grounding by showing A/C clutch "ON." If the ECM sensed voltage from circuit 67, the cooling fan will be energized.


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

1. The ECM will energize the A/C relay only when the engine is running. This test will determine if the relay or circuit 458 is faulty.
2. In order for the clutch to properly be engaged, the low and high pressure switches must be closed so the A/C request (12 volts) will be present at the ECM.
3. A short to ground in any part of the A/C request or clutch control circuits may be the cause of a blown fuse.
4. With the engine idling and A/C "ON," the ECM should be grounding circuit 458, which should cause the test light to be "ON."
5. This determines if the signal is reaching the low pressure switch on circuit 66 from the A/C control panel. The signal should only be present when the A/C mode or defrost mode has been selected.


DIAGNOSTIC AIDS:

If the complaint was insufficient cooling, the problem may be caused by an inoperative cooling fan or A/C pressure fan switch. The engine cooling fan should turn "ON" when A/C pressure exceeds a given value to open the switch, which will cause the ECM to energize the cooling fan relay. See ELECTRIC COOLING FAN (CHART C-12), for cooling fan diagnosis. The A/C clutch will be disengaged if the power steering pressure signal (high pressure) is defected by the ECM. See POWER STEERING PRESSURE SWITCH (CHART C-1E).