Component Diagnostic Charts/Tests

Chart C-10:

Wiring Diagram For A/C Clutch Control:

CIRCUIT DESCRIPTION:

When an A/C mode is selected on the A/C control switch, ignition voltage is supplied through the A/C request circuit to the ECM. With sufficient system pressure, the low pressure switch will be closed and complete the circuit to the high pressure cut-off switch, and to circuits 603 and 604. When a request for A/C is sensed by the ECM, the ECM will ground circuit 459 which energizes the A/C clutch control relay. The relay will then send current through circuits 604 and 59 to engage the A/C compressor clutch. A "Scan" tool will display circuit 459 by showing A/C clutch "ON." If the ECM sensed voltage from circuit 603, the cooling fan will be energized.

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

1. The A/C compressor clutch should not engage until three seconds after the engine is started.

2. See HEATING VENTILATION AND AIR CONDITIONING for a basic A/C problem.

3. A blown HTR-A/C fuse could be caused by a short to ground from the ignition switch to the compressor.

DIAGNOSTIC AIDS:

Both pressure switches are located at the rear of the A/C compressor. The low pressure switch connector can be identified by a blue insert and the high pressure switch connector by a red insert. See COMPONENT LOCATIONS for the location of the A/C control relay. The low pressure switch opens and closes at approximately 8.0 psi (55.0 kPa) and 47.0 psi (324 kPa) respectively. At approximately 430 psi (2960 kPa), the A/C high pressure switch opens to disengage the A/C clutch, which prevents system damage.