The air delivery controls are divided into eight areas:

HVAC Control Module

The HVAC control module receives power from two separate sources. The underhood junction block provides keep alive memory (KAM) power through the battery positive circuit. The left instrument panel (I/P) fuse block provides a device on signal to the HVAC control module through the ignition 3 voltage circuit. The ignition 3 voltage circuit also powers the 5 volt regulator. The Class 2 serial data circuit provides a data circuit for scan tool communication and transmit and receive Class 2 messages. Personalization of HVAC operation is not available with this vehicle.

The HVAC control module processes information provided from various air temperature sensors, actuators and driver inputs to ensure that accurate HVAC operation is provided. The HVAC system can work in manual mode and automatic mode. The vehicle operator selects which mode is selected through the HVAC control module switch inputs.

When in automatic mode, blower speed, mode position and air temperature settings are calculated based on the air temperature setting. When in manual mode the blower speed and air delivery mode can be changed. The HVAC control module still tries to maintain the air temperature unless it is set to full cold or full hot temperatures. When at these full extremes the HVAC control module will position the air temperature actuator to its full cold or hot position depending on the selected air temperature.

Front Auxiliary HVAC Control Assembly

The front auxiliary HVAC control assembly provides inputs to the rear auxiliary HVAC control module. It is located in the overhead console so that front seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode, air temperature settings and control of which control unit will operate the auxiliary HVAC system. When the REAR position is selected, inputs from this control assembly will not be processed by the rear auxiliary HVAC control module. When OFF position is selected the auxiliary system is inoperative. The module is turned on by ignition voltage from the ignition 3 voltage circuit.

Rear Auxiliary HVAC Control Module

The rear auxiliary HVAC control module processes and controls all aspects of the automatic auxiliary HVAC system. The module has communication with the HVAC control module via 2 keyboard data display (KDD) communication circuits. The system receives inputs from the auxiliary upper air temperature sensor, auxiliary lower air temperature sensor, infrared temperature sensor, and feed back signals from auxiliary mode actuator and the auxiliary air temperature actuator. Along with inputs from the front auxiliary HVAC control assembly. The outputs are the auxiliary air temperature actuator, auxiliary mode actuator, auxiliary blower motor control processor and data communication with the HVAC control module. The module is turned on by ignition voltage from the ignition 3 voltage circuit.

The blower motor forces air to circulate within the vehicle's interior. The vehicle operator determines the blower motor's speed by placing the blower motor switch in a desired speed position or by selecting automatic operation. The blower motor will only operate if the blower motor switch is in any position other than OFF, and the ignition switch is in the RUN position. The blower motor and mode switches are located on the front of the HVAC control module.

Power is provided to the blower motor from the underhood junction block through the battery positive voltage circuit. The HVAC control module receives power from the ignition 3 voltage and battery positive voltage circuits. Ground is provided by the right instrument panel junction block through the ground circuits.

When any blower speed is selected, the HVAC control module sends a pulse width modulated (PWM) signal to the blower motor on the blower speed control circuit. In manual operation, once a blower speed is selected, the blower speed remains constant until a new speed is selected. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature.

The auxiliary blower motor circulates the air at the rear of the vehicle. The vehicle operator determines the auxiliary blower motor's speed by placing the blower motor switch in a desired speed position. The auxiliary blower motor switch controls the auxiliary blower motor speed. Three relay blower motor speed control circuits enable one of three relays to provide power to the blower motor. The blower motor switch grounds the selected relay. Each relay's control and load power is provided by the ignition and battery positive voltage circuits. Both the low and medium speed relays connect to the auxiliary blower motor through a resistor assembly. The resistor assembly creates a voltage divider circuit with the auxiliary blower motor to select the auxiliary blower motor speed. The high speed relay is connected directly to the auxiliary blower motor. The primary HVAC control module located in the dash does not control the auxiliary HVAC system.

The auxiliary blower motor circulates the air at the rear of the vehicle. The auxiliary blower motor can be controlled by either of the auxiliary HVAC controls. The primary HVAC control module located in the dash does not control the auxiliary HVAC system. If the vehicle does not have a sunroof (CF5), then the front auxiliary controls must be set to the rear position for the rear auxiliary controls to operate. The vehicle operator determines the blower motor's speed by placing a blower motor switch in a desired speed position or by selecting automatic operation. The auxiliary blower motor will only operate when the ignition is in the RUN position and an auxiliary HVAC control is set in any position other than OFF.

Power is provided to the auxiliary blower motor from the underhood junction block through the battery positive voltage circuit and IP wiring harness junction block. The auxiliary HVAC control module receives power by the ignition 3 voltage circuit through the right instrument panel junction block through the ground circuits.

When any blower speed is selected on either of the auxiliary control modules send a pulse width modulated (PWM) signal to the auxiliary blower motor speed control circuit. In manual operation, once a blower speed is selected, the auxiliary blower speed remains constant until a new speed is selected. In automatic operation, the auxiliary HVAC module will determine what auxiliary blower speed is necessary in order to maintain desired temperatures. At startup in colder temperatures, the auxiliary blower motor will not begin operation at the same time as the primary blower motor. Warm coolant is circulated to the auxiliary heater core before the blower motor begins operating.

When a mode switch position is selected, a signal is sent from the HVAC control module to the mode actuator through the mode door control circuit. The mode actuator moves the mode door to the desired position.

When the mode door moves to a desired position, a variable resistor within the actuator is used to create the mode door position signal. The HVAC module uses the mode door position signal to determine the actual mode door position. The left instrument panel fuse block provides power to the mode actuator through the ignition 3 voltage circuit and the IP wiring harness junction block. Power and ground are provided to the HVAC control module by the fuse block through the ignition 3 voltage circuit and the ground circuits through the right instrument panel junction block. A 5 volt reference signal is sent to the actuator through the 5 volt reference circuit, through the right instrument panel junction block, to the mode actuator.

If the vehicle has a sunroof (CF5), then the auxiliary mode actuator can only be controlled by the front auxiliary HVAC control assembly. The primary HVAC control module located in the dash cannot control the auxiliary HVAC system. The vehicle operator determines the mode setting by placing a mode switch in a desired mode position. Only upper and lower vent positions are available at the rear of the vehicle. When a mode setting is selected, a signal is sent from the front auxiliary control assembly to the mode actuator through the mode door control circuit. The auxiliary mode actuator moves the auxiliary mode door to the desired position. Power and ground is supplied to the mode actuator by the ignition and ground circuits.

Depending upon the auxiliary HVAC system content, the auxiliary mode actuator can be controlled by either of the auxiliary HVAC controls. The primary HVAC control module located in the dash does not control the auxiliary HVAC system. If the vehicle does not have a sunroof (CF5), then the front auxiliary controls must be set to the rear position for the rear auxiliary controls to operate. The vehicle operator determines the mode setting by placing a mode switch in a desired speed position. Only upper and lower vent positions are available in the rear of the vehicle.

When a mode position is selected on either of the auxiliary HVAC controls, a signal is sent from the auxiliary HVAC controls to the auxiliary mode actuator through the mode door control circuit. The auxiliary mode actuator moves the auxiliary mode door to the desired position. When the auxiliary mode door moves to a desired position, a variable resistor within the actuator is used to create the mode door position signal. The HVAC module uses the mode door position signal to determine the actual auxiliary mode door position. Power and ground are provided to the HVAC control module by the fuse block through the ignition 3 voltage circuit and the ground circuits through the right instrument panel junction block. A 5 volt reference signal is sent to the actuator through the 5 volt reference circuit, through the right instrument panel junction block, to the auxiliary mode actuator.

When air recirculation is selected, a signal is sent from the HVAC control module to the recirculation actuator through the recirculation door control circuit. The recirculation actuator closes the recirculation door in order to circulate the air within the vehicle. The outside air switch opens the recirculation door in order to route outside air into the vehicle.

Regardless of the blower motor switch position, recirculation is available only in the vent and bi-level mode switch positions. Including the OFF position. The mode switch must be placed in either the vent or bi-level position before the blower motor switch is placed in the OFF position. In order to reduce windshield fogging, outside air is circulated when the mode switch is in the defrost, floor, and mix-blend positions. If the recirculation switch is pressed into the ON position when the mode switch is in an unavailable mode position, then the recirculation switch LED will flash 3 times.

When the recirculation door moves to a desired position, a variable resistor within the actuator is used to create the recirculation door position signal. The HVAC module uses the recirculation door position signal to determine the actual recirculation door position. The left instrument panel fuse block provides power to the recirculation actuator through the ignition 3 voltage circuit and the IP wiring harness junction block. Power and ground are provided to the HVAC control module by the fuse block through the ignition 3 voltage circuit and the ground circuits through the right instrument panel junction block. A 5 volt reference signal is sent to the actuator through the 5 volt reference circuit, through the right instrument panel junction block, to the recirculation actuator.

When the automatic setting has been selected, the HVAC control module will recirculate air whenever system temperature performance is insufficient to provide the desired temperature. The recirculation switch LED will not be illuminated. If either the outside air or recirculation switch is pressed during automatic operation, then automatic operation will be over ridden. The appropriate recirculation or outside air switch LED will be illuminated. The recirculation door will be opened or closed depending upon the selected override. When the ambient air temperature is below 4°C (40°F) the recirculation override of the automatic setting will only be available for 10 minutes.

When the automatic setting has not been selected, only the outside air or recirculation switch will be used to determine the recirculation door position. When the ambient air temperature is below 4°C (40°F) any recirculation selection will only be available for 10 minutes.

The A/C high pressure recirculation switch can cause the HVAC system to recirculate air. When the high side pressure reaches 2206-2620 Kpa (320-380 psi), the PCM will place the HVAC system in recirculation mode. The high side pressure is lowered when the inside air cools the refrigerant within the A/C evaporator. When the high side pressure reaches 1447-1861 Kpa (210-270 psi), the PCM will place the HVAC system out of recirculation mode.

The Automatic HVAC system has the option of being configured with either a manual or automatic auxiliary system. The number of auxiliary HVAC controls is dependent upon whether or not the vehicle is equipped with a sunroof (CF5). An automatic auxiliary HVAC system is only available with an automatic primary HVAC system without a sunroof. A manual auxiliary HVAC system is only available with an automatic auxiliary primary HVAC system with a sunroof.

The automatic primary and auxiliary HVAC systems communicate using keyboard data display (KDD) protocol. The automatic primary system communicates with the rear auxiliary HVAC control module. The manual auxiliary system is independent of the automatic primary HVAC system.

The automatic HVAC system will maintain the interior temperature of the vehicle by controlling the blower motor, air temperature, mode and recirculation actuators to achieve the desired temperature. For full automatic operation, both the blower and mode switches must be in the AUTO position and the air temperature set between 19°C (66°F) and 28°C (82°F). Blower speeds will be gradually increased or decreased, and can be reduced based on vehicle speed in order to maintain airflow into the vehicle. At start up, the automatic HVAC system will use to the last settings used prior to vehicle shut down.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. At initial vehicle start up, the blower motor is not turned on until the coolant reaches a predetermined temperature. If the coolant does not warm up within a preset time, the blower will be activated. The HVAC system can quickly warm up the vehicle when the temperature and blower motor settings are set to maximum and outside air and floor modes are selected. Once the desired temperature is reached, the blower motor will slow down, discharge temperatures will be lowered, and the mode actuator will remain in the floor setting. The system can be placed in bi-level if the ambient temperature is near 7-10°C (45-50°F). Regardless of mode selection, some air will be diverted to the defrost setting to keep window fogging at a minimum.

If the ambient air temperature is less than 2°C (35°F) and the coolant temperature is less than 10°C (50°F), then a 75 second purge will occur. The purge is performed in order to reduce window fogging until the coolant warms up. The purge will begin as soon as the coolant temperature reaches 4°C (40°F). The mode door will move to the defrost position and the blower motor will be near half speed.

In warm temperatures, the automatic HVAC system will provide A/C in the most efficient manner. The HVAC system can quickly cool down the vehicle when the temperature is set to minimum, blower motor is set to maximum, and recirculation and vent modes are selected. Once the desired temperature is reached, the blower motor will slow down, discharge temperatures will be raised, and the mode actuator will be switched to bi-level for better passenger comfort. The recirculation actuator can be partially opened to assist in temperature control. Regardless of mode selection, some air will be diverted to the floor setting to keep occupant comfort at a maximum.