Circuit Description
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The engine control module (ECM) monitors the high side refrigerant pressure through an A/C refrigerant pressure sensor. When the pressure is high, the signal voltage is high. When the pressure is low, the signal voltage is low. When pressure is high, the ECM commands the cooling fans on. When pressure is too high or too low, the ECM will not allow the A/C compressor clutch to engage. The ECM sends the A/C pressure data to the body control module (BCM) over the GM LAN serial data circuit. This keeps the high side pressure in a normal operating range. This will prevent the A/C compressor clutch from disengaging under normal operating conditions. The BCM will not request A/C compressor clutch engagement if the A/C pressure is too high.