Part 1 of 2

Chart C-10, A/C Compressor Clutch Control Circuit Diagnosis (1 Of 2):

A/C Compressor Clutch Circuit Diagram:

CIRCUIT DESCRIPTION
The A/C relay is ECM controlled to delay A/C clutch engagement 0.4 seconds after A/C is turned "ON". This allows the IAC to adjust engine rpm before the A/C clutch engages. The ECM may also apply the A/C clutch during cranking to prevent A/C slugging. The ECM also causes the relay to disengage the A/C clutch during WOT operation. The A/C relay is energized when the ECM provides a ground path for CKT 459. The A/C refrigerant pressure is used to determine high and low pressure in the system and also turns "ON" the coolant fan when it is needed.


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

1. The ECM will only energize the compressor clutch relay when the engine is running. This test will determine if the relay of CKT 459 is faulty.

2. Determines if ECM is receiving the A/C request signal from the A/C control panel (circuit 66). Signal should be present when the selector is in an A/C or defrost position.

3. If the ECM is receiving a high pressure indication from the Power Steering Pressure Switch, the A/C clutch will be disengaged.


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.