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 Class 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 A/C 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