Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cool air to the interior of the vehicle. The A/C system will also remove humidity from the interior of the vehicle. The A/C system can operate regardless of the temperature setting as long as the ambient temperature is above 3°C (37°F). If the A/C compressor is turned off due to low ambient temperatures, then the compressor will not be activated until temperatures reach 6°C (42°F).

The vehicle operator can determine the level of heated air or cool air by toggling the temperature switch located on the HVAC control module, to any setting. The air temperature switch can change the vehicle's air temperature regardless of the HVAC mode setting, heater OR A/C. If the temperature switch is toggled, then the VF will display the current set temperature for approximately 5 seconds. Continued toggling of the temperature switch within 5 seconds will cause the displayed temperature to be increased or decreased.

If the selected air temperature is placed at any other temperature than 32°C (90°F), then, the air temperature actuator position is regulated to achieve the desired set temperature. If a warm air temperature is needed, then the IPM will monitor the lower duct temperature sensors, the inside air temperature sensor and the solar sensors to correctly position the air temperature actuators. The IPM will only change the position of the air temperature actuators to maintain the set temperature. The blower speeds and mode setting are not adjusted.

If the temperature switch is toggled to a VF display of 32°C (90°F), then the IPM will move the air temperature actuators to the full warm air position. The blower speed and mode will remain in the last known manual position on the HVAC control module. If the HVAC control module is in the AUTO mode, then the blower motor will run at full speed, and the IPM will ignore the lower duct temperature sensors, sunload sensors, and inside air temperature sensor at this time. Toggling the temperature switch to a VF display of 15°C (60°F) will operate the HVAC system in maximum cooling. The blower motor is at high speed; mode is in the PANEL position. The air temperature actuators are moved to the full cold position, and recirculation is drawing air from inside of the vehicle. The IPM will ignore the upper duct temperature sensors, sunload sensors, and inside air temperature sensor at this time. The AUTO LED will not illuminate. After setting the temperature switch above 15°C (60°F) the AUTO switch will have to be pressed to activate the automatic HVAC system and the AUTO LED will illuminate.

In all A/C mode settings, the IPM receives an input from the HVAC control module. In order for the Powertrain Control Module (PCM) to internally ground the A/C clutch relay control circuit, the Body Control Module (BCM) and the PCM must communicate to each other over the Class 2 serial data circuits.

The PCM monitors:
^ A/C refrigerant line pressure
^ Engine coolant temperature

The BCM monitors:
^ A/C refrigerant line pressure
^ Engine coolant temperature
^ Battery voltage
^ A/C request from the IPM

The BCM will request A/C operation from the PCM if these parameters are within normal operating limits.

The PCM turns on the A/C compressor by providing a path to ground through the A/C compressor clutch relay control circuit. Ignition 3 voltage is supplied through the A/C compressor clutch supply voltage circuit when the relay closes.

When the compressor disengages, the A/C compressor clutch diode absorbs the voltage surge. This surge results from the collapsing magnetic field of the compressor clutch coil.

The PCM will engage the compressor clutch anytime 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
^ Idle Quality
^ A/C refrigerant pressure sensor is more than 2968 kPa (430 psi)
^ A/C refrigerant pressure sensor 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) for the LX5 and 126°C (259°F) for the L47
^ Transmission shift
^ Engine torque load

For a description of the RPO Code(s) shown in this article/images refer to the RPO Code List found at Vehicle/Application ID. RPO Codes