A/C Mode

The purpose of the Air Conditioning (A/C) system is to provide cool air and remove humidity from the interior of the vehicle. The A/C compressor is engaged when the HVAC control module is in the following modes:
^ Defog
^ Front Defrost
^ Heater
^ A/C

The A/C system operates regardless of the temperature setting, as long as ambient temperature is above 3°C (38°F). The vehicle passenger can control the temperature offset by adjusting the right air temperature switch assembly 3°C (5°F) from the primary setting.

The HVAC control module is the interface between the vehicle operator and the IPM. The HVAC control module receives power from the IP fuse block on the ignition 3 voltage circuit. The IPM is also powered from the IP fuse block through the ignition 3 voltage circuit along with the battery positive voltage circuit. Both modules are grounded through the ground circuit.

When the A/C request is selected, the IPM receives an input from the HVAC control module. The IPM and HVAC control module communicate over the driver HVAC control assembly signal and the driver HVAC control assembly clock signal circuits. In order for the Powertrain Control Module (PCM) to internally ground the A/C clutch relay control circuit, the Body Control Module (BCM) and PCM must communicate to each other over the class 2 serial data circuits. The PCM monitors A/C refrigerant line pressure and engine coolant temperature. This information is placed on the class 2 serial data circuit and is monitored by the BCM. The BCM monitors the A/C line pressure, the engine coolant temperature, the battery voltage, and the A/C request input from the IPM. The BCM will request A/C operation from the PCM if these parameters are within normal operating limits and the HVAC control module is requesting A/C operation.

The PCM turns on the A/C compressor by providing a path to ground through the A/C clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay internally of the underhood fuse block. Once the relay closes its internal switch, power from the battery is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. Whenever the compressor is turned off, the A/C compressor clutch diode provides a path for the voltage spike resulting from the collapsing magnetic field of the compressor clutch coil. The ground circuit provides a pathway to ground for the compressor. The A/C clutch relay control circuit is grounded internally within the PCM.