General Information

HVAC Compressor Controls Circuit Description


The Instrument Panel Integration Module (IPM) sends a Class 2 message to the Dash Integration Module (DIM). The DIM monitors, A/C refrigerant pressure, low side temperature, and engine coolant and battery voltage to ensure conditions are correct for compressor operation. If all conditions are correct the DIM sends a Class 2 message to the Powertrain Control Module (PCM) with the system operating in any mode but OFF.

Under normal operating conditions, the PCM then grounds the A/C compressor control relay coil and the relay energizes. Voltage is supplied to the A/C compressor clutch through a fuse and the A/C compressor clutch relay contacts.

The A/C compressor clutch engages and the compressor operates.

If the PCM determines that engine load should be reduced, such as during full throttle conditions, it will de-energize the A/C compressor relay to disengage the compressor even though the message signal from the Dash Integration Module (DIM) is still present. The compressor contains an internal thermal switch. This switch opens when the compressor temperature exceeds 155°C (311°F). The compressor thermal switch closes when the compressor temperature reaches approximately 125°C (257°F).

The compressor thermal switch is serviced by replacement of the compressor.