PCM Controlled Air Conditioning

The A/C system uses a scroll type compressor controlled by the PCM to meet the cooling demands. The A/C clutch system consists of the following components:
^ The Instrument Panel Integration Module (IPM) (HVAC controller)
^ The Dash Integration Module (DIM)
^ The A/C pressure sensor
^ The low side temperature sensor (monitors evaporator core temperature)
^ The A/C relay
^ The A/C compressor clutch
^ The PCM

When an A/C mode is selected, the IPM sends a Class 2 message to the DIM. The DIM then checks the A/C pressure sensor, the low side temperature, the engine coolant temperature, and the system voltage. If all the conditions are right to allow compressor operation, the DIM sends an A/C request signal via Glass 2 to the PCM. The PCM energizes the A/C relay coil by grounding the A/C relay control circuit.

This closes the relay contacts and applies a fused battery voltage to the A/C compressor clutch. The PCM enables the compressor clutch whenever the engine is running and A/C is requested unless one or more of the following conditions are present:
^ The system voltage is less than 8 volts.
^ The A/C pressure sensor indicates a low or a high A/C pressure condition.
^ High power steering load
^ The throttle angle is more than 90 percent.
^ The ambient air temperature is less than 4°C (39°F).
^ The evaporator core temperature is less than -2°C (28°F).
^ The engine coolant temperature is more than 126°C (259°F).

PCM DTCs P0532, P0533, P0560, P0562, P0563, P1545 and P1639 affect the A/C operation. Refer to the appropriate DTC tables to diagnose any PCM set DTCs. The HVAC system may contain DTCs that also affect the NC operation. Refer to the appropriate DTC table in Heating and Air Conditioning to diagnose any HVAC DTCs.

The PCM controlled air conditioning table diagnoses the electrical portion of the A/C compressor clutch circuit when no DTC is set. To diagnose the refrigerant portion of the HVAC system, refer to Heating and Air Conditioning (HVAC). A scan tool will be used in diagnosing the system. The scan tool has the following functions to aid diagnosis:
^ Displays the A/C request status
^ Displays the A/C pressure sensor input to the PCM
^ Displays the PCM commanded state of the A/C clutch
^ Can override the A/C request and energize the A/C relay