PCM Controlled A/C

The PCM controlled A/C is controlled by the HVAC control assembly, Body Control Module (BCM), and the Powertrain Control Module (PCM). When an A/C mode is selected on the HVAC control assembly a signal is sent to the BCM, the BCM then sends out an A/C request signal on the Class II Serial Data Circuit to the PCM. The PCM monitors the engine coolant through the Engine Coolant Temperature (ECT) sensor, and the A/C pressure through the A/C pressure sensor. If conditions are optimal for compressor operation, the PCM provides a ground path for the A/C compressor relay coil which closes the A/C relay contacts and ignition positive voltage is applied to the A/C compressor clutch. For more information concerning the A/C system refer to PCM Controlled Air Conditioning Description, Body Control System Operation in Body Control System, HVAC Compressor Controls Circuit Description in Heating and Air Conditioning.