Controls and Compressor Cycling

Climate control commands are inputted through the HVAC  control module and on vehicles equipped with Sony Sound inputs can also be commanded through voice commands or the touch screen.

When the A/C  is requested, the HVAC  control module sends the message over the Medium Speed Controller Area Network (MS-CAN) to the BCM  . The BCM  then forwards the message to the PCM  over the High Speed Controller Area Network (HS-CAN).

When A/C  is requested and A/C  line pressures allows, 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.

The evaporator discharge air temperature sensor is an input to the BCM  and is relayed to the PCM  over the High Speed Controller Area Network (HS-CAN). The evaporator discharge air temperature sensor prevents icing of the evaporator by measuring the temperature of the airflow immediately after the evaporator. An accurate evaporator temperature is critical for compressor engagement. The PCM  uses the temperature measurement to regulate the on and off time of the A/C  compressor to maintain the evaporator temperature within an acceptable temperature range.

The PCM  monitors the discharge pressure measured by the A/C  pressure transducer. The PCM  interrupts A/C  compressor operation in the event the A/C  pressure transducer indicates high system discharge pressures. It is also used to sense low charge conditions. If the pressure is below a predetermined value for a given ambient temperature, the PCM  does not allow the A/C  clutch to engage.

The HVAC  control module adjusts the air inlet door depending on the humidity measured by the in-vehicle temperature and humidity sensor. If the vehicle cabin becomes too humid and recirculated air is not selected, the HVAC  control module adjusts the air inlet door to allow more recirculated air. When the humidity level drops, it adjusts back to fresh air. The HVAC  control module also adjusts the system based on in-vehicle temperature.

The autolamp/sunload sensor supplies information to the HVAC  control module indicating the intensity of the sun on the vehicle and the HVAC  control module adjusts the system based on the intensity.