Control System Logic

Controls and Compressor Operation 

All customer climate control requests for the EATC system are inputted through the HVAC control module.

Heating and Ventilation 

The heating and ventilation system:

• controls the temperature of the air inside the vehicle.
• reduces the relative humidity of the air inside the vehicle (during A/C compressor operation).
• delivers heated or cooled air to maintain the vehicle interior temperature and comfort level.

Electric Booster Heater 

For information on the electric booster heater operation and diagnostics, refer to Auxiliary Climate Control System .

A/C (Air Conditioning) Request 

When the A/C is requested, the HVAC control module sends the message over the MS-CAN to the IPC. The IPC sends the A/C request to the PCM through the HS-CAN.

When an A/C request is received by the PCM, the PCM engages the A/C clutch relay when:

• the refrigerant pressure is not excessively high or low.
• the engine coolant temperature is not excessively high.
• the ambient air temperature is above approximately -2.2 °C (28.4 °F).
• a Wide Open Throttle (WOT) condition is not present.
• the evaporator discharge air temperature is above approximately 1.5 °C (35 °F).

Compressor Clutch 

When A/C is requested and all conditions are within normal parameters, a ground is provided to the A/C clutch relay coil from the PCM, energizing the A/C clutch relay. When the PCM energizes the relay, voltage is supplied to the A/C compressor clutch field coil from the relay.

Sensor Inputs 

The Ambient Air Temperature (AAT) sensor and the evaporator temperature sensor are inputs to the IPC and the information is relayed to the PCM over the HS-CAN. If the temperature is below a predetermined value, the PCM does not allow the A/C clutch to engage.

The sunload sensor is an input to the HVAC control module indicating the intensity of the sun on the vehicle and the HVAC control module compensates high sun load with higher blower and reduced discharge temperatures.

The in-vehicle temperature sensor is an input to the HVAC control module. The HVAC control module adjusts the system based on the temperature of the passenger compartment air.

The center register air discharge temperature sensor and the footwell air discharge temperature sensor are inputs to the HVAC control module and the HVAC control module adjusts the system based on the outlet air temperature.