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A/C Request Circuit Diagnosis

Schematic:






CIRCUIT DESCRIPTION:
The A/C clutch relay is PCM controlled to delay A/C clutch engagement after the A/C is turned ON. This allows the PCM to adjust engine RPM before the A/C clutch engages. The PCM will engage the A/C clutch any time A/C has been requested unless any of the following conditions exist:
^ High coolant temperature
^ Low A/C system pressure
^ High A/C system pressure
^ Wide open throttle
^ High engine RPM

When the heater and A/C control is placed in the A/C mode and the engine is operating, a 12 volt signal is sent to the PCM. When the PCM receives this signal the PCM will ground the A/C clutch relay control circuit to energize the A/C relay. This is shown on the scan tool as A/C request YES.

When a request for A/C has been detected by the PCM, the PCM will ground the A/C clutch relay control circuit, the relay contacts will close, and current will flow through the relay to the A/C compressor clutch.

DIAGNOSTIC AIDS

IMPORTANT:
^ Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
^ For any test that requires probing the PCM or component harness connectors, use the J 35616-A connector test adapter kit. Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Diagrams.

Ensure no PCM DTCs are stored before using this table. The PCM will not activate the A/C clutch with a stored DTC.

TEST DESCRIPTION


Steps 1 - 5:





Steps 6 - 13:






The numbers below refer to numbers on the diagnostic table.
2. A/C DTCs will disable the A/C system. Repair A/C DTCs before proceeding.
3. The request circuit is shorted to a voltage if the scan tool displays A/C request as YES.
5. A condition exists with the request circuit between the PCM and the HVAC Programmer, or the HVAC Programmer is malfunctioning if the test lamp did not illuminate.
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