Part 2 of 2

Chart C-10, A/C Compressor Clutch Control Circuit Diagnosis (2 Of 2):

A/C Compressor Clutch Circuit Diagram:

CIRCUIT DESCRIPTION
The A/C clutch control relay is energized when the ECM provides a ground path through CKT 459 and A/C is requested. A/C clutch is delayed about 0.3 seconds after A/C is requested. This will allow the IAC to adjust engine RPM for the additional load.

The ECM will temporarily disengage the A/C clutch relay for calibrated times for one or more of the following:
^ Hot engine restart.
^ Wide open throttle (TP sensor over 90%).
^ Power steering pressure high (open switch).
^ Engine speed excedes 6,000 rpm.
^ During IAC reset procedure.

The A/C clutch relay will remain disengaged when a DTC 66 is present if pressure is out of range or there is no A/C request signal due to an open A/C select switch or circuit.


TEST DESCRIPTION
Numbers below refer to circled numbers on diagnostic chart.

1. Determines is the pressure transducer signal indicates pressures out of range causing the compressor clutch to disengage.

2. With the engine stopped and field service mode activated, the ECM should be completing relay circuit 459, which should cause the test light to be "ON".


DIAGNOSTIC AIDS
If the complaint is insufficient cooling, the problem may be an inoperative engine cooling fan. Refer to chart C-12. If cooling fans operate properly, problem may be A/C pressures outside of range, or faulty pressure transducer indicating pressure out of range (43 - 428 psi). Monitor A/C pressure with "SCAN" tool and compare to actual readings with A/C manifold/gauges. "SCAN" readings should be within 20 psi of actual pressure. If not see Code 66 diagnostic chart, or replace pressure transducer. If actual pressures are out-of-range, refer to HEATING AND AIR CONDITIONING.