Control System Logic

Controls and Compressor Operation 

All customer requests for the Electronic Manual Temperature Control (EMTC) system come through the HVAC control module.

A/C (Air Conditioning) (if equipped) Request 

The HVAC control module uses a dedicated wire to send the A/C request message 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 -6.6 °C (20 °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. The A/C pressure transducer is an input to the PCM. If the temperatures are below a predetermined value, or the system pressure becomes too high or too low, the PCM does not allow the A/C compressor clutch to engage.

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, if equipped).
• delivers heated or cooled air to maintain the vehicle interior temperature and comfort level.