General Information

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 A/C or FRONT DEFROST mode. The A/C system can operate regardless of the temperature setting, as long as outside ambient temperature is above 3°C (37°F). If the driver tries to turn OFF the A/C while in FRONT DEFROST mode, the A/C OFF text on the VF display will flash, indicating that this is not allowed. If the A/C compressor is turned off due to low outside ambient temperatures, the compressor will not be activated until temperatures reach 6°C (42°F). The vehicle passenger can adjust their temperature by turning the right air temperature switch. The driver and passenger can select any temperatures from full hot, 32°C (90°F), to cold, 16°C (60°F), independently. The HVAC control module is the interface between the vehicle operator and the IPM. The HVAC control module receives power from the rear fuse block on the ignition 3 voltage circuit. The IPM is also powered from the rear fuse block through the ignition 3 voltage circuit along with the battery positive voltage circuit. Both modules are grounded by the ground circuit. The IPM and HVAC control module communicate back and forth 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 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, engine coolant temperature, battery voltage along with the A/C request input from the IPM. The DIM will request A/C operation from the PCM if these parameters are within normal operating limits and the IPM 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 within 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 path to ground for the compressor. The A/C clutch relay control circuit is grounded internally within the PCM.

The PCM will engage the A/C compressor clutch any time the engine speed is below 5000 RPM and the A/C is requested unless any of the following conditions exist:
^ Throttle angle is at 100 percent (WOT).
^ Vehicle launch, acceleration from a stop.
^ Idle quality
^ The A/C refrigerant pressure sensor is more than 2968 kPa (430 psi) or is less than 255 kPa (35 psi).
^ Engine speed is more than 5500 RPM.
^ Engine coolant temperature (ECT) is more than 121°C (250°F).
^ Transmission shift
^ Engine torque load