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 system is engaged when the HVAC control module is in any mode. The A/C system can operate regardless of the temperature setting, as long as outside ambient temperature is above 4°C (39°F). The passenger and can adjust the temperature offset by adjusting the right air temperature switch. Passenger temperatures can be set anywhere between 16°C (60°F) to 32°C (90°F). The temperature switches operate independently from each other. For best results, the passenger offset should only be 2°C (4°F) cooler or warmer than the primary setting.

Power and ground are provided to the HVAC control module by the underhood fuse block on the battery positive and ground circuit.

When the A/C request is selected, a signal is sent from the HVAC control module to the Powertrain Control Module (PCM). In order for the PCM to internally ground the A/C clutch relay control circuit, the Dash Integration Module (DIM) and PCM must communicate with 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 DIM. The DIM looks at the A/C line pressure, the A/C refrigerant low temperature sensor, engine coolant temperature, battery voltage along with the A/C request input from the HVAC control module. The DIM 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. If there is a malfunction in the A/C system, the driver information center will read SERVICE A/C SYSTEM to alert the vehicle operator that there is a malfunction with the A/C system.

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 and thermal switch. The ground circuit provides a pathway to ground for the compressor. The A/C clutch relay control circuit is grounded internally within the PCM.

The PCM will open the A/C clutch relay control circuit when coolant temperatures get too hot. When temperatures reach 163°C (262°F), the PCM will open the A/C clutch relay control circuit. When coolant temperatures lower to 124°C (255°F), the PCM will ground to the A/C clutch relay control circuit again. When the PCM reads wide open throttle, the PCM will shut off the compressor for 20 seconds.