The air delivery description and operation are divided into five areas:

HVAC Control Module

The HVAC control module is a class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The ignition 3 voltage circuit provides a device on signal. Three integrated potentiometers control mode and air temperature door positions and blower motor speed. The control assembly communicates the mode door position to the vacuum control assembly through 5 solenoid control circuits. The control module supports the following features:

The blower motor circulates air through the vehicle's interior. The vehicle operator determines the blower motor's speed by pressing the blower motor switch manually or by using the automatic mode. The blower motor will only operate if the blower motor switch is in any position other than OFF, as long as the ignition switch is in the RUN position. The blower motor and mode switches are located within the HVAC control module.

Power is provided to the blower motor from the blower motor control processor through the blower motor supply voltage circuit. The blower motor control processor receives power from the instrument panel fuse block through the battery positive voltage circuit. Ground is provided by the blower motor control processor, ground circuit and splice pack.

The HVAC control module receives power from the instrument panel fuse block on the ignition 3 voltage circuit along with the battery positive voltage circuit. The module is grounded by the ground circuits and splice pack. The HVAC control module communicates directly to the powertrain control module (PCM) on the class 2 serial data circuit through the star connector.

When any blower speed is selected, whether manual or automatic, the blower motor control processor will control blower motor speeds based on voltage signals from the HVAC control module. A 5-volt signal is sent from the blower motor control processor to the HVAC control module on the blower motor speed control circuit. When the driver manually selects a blower speed or the automatic HVAC system determines a needed speed, the HVAC control module will provide a pulse width modulated (PWM) ground. The remaining voltage at the blower motor control processor is used to provide a blower motor speed signal. A 12-volt signal is sent to the blower motor from the blower motor control processor on the blower motor supply voltage circuit. The blower motor control processor varies the ground on the blower motor control circuit internally with a separate PWM signal. An open circuit, short to ground or short to battery on the blower motor speed control circuit will disrupt the PWM signal and cause the blower motor to not operate. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature.

When in manual mode, the driver can change the blower speed by pressing the blower motor switch. If the driver presses the blower motor switch once, the blower speed will increase/decrease 1 level. Holding the blower motor switch down will increase/decrease the blower speed to the maximum/minimum speed.

Off

Press the OFF switch to turn OFF the HVAC system. When the vehicle is moving, air flowing over the vehicle increases the air pressure just ahead of the windshield. This forces air into the HVAC air inlet and out through any desired mode setting. The HVAC control module attempts to match the inside air temperature and HVAC control module selected temperatures. Driver set temperature and passenger temperature offset can be adjusted. Since the A/C compressor is not running, the incoming air may be warmed but not cooled.

When the mode switch is pressed, a signal is sent from the HVAC control module to the vacuum control assembly. The HVAC control module will provide ground for the necessary mode actuator solenoid, connecting the desired mode actuator to vacuum. The instrument panel fuse block provides power to the vacuum control assembly through the ignition 3 voltage circuit. Ground is provided by the HVAC control module.

Mode Switch

Use the MODE switch in order to change the air delivery mode in the vehicle. Selection of the MODE switch when in AUTO mode will lock in the air flow mode that AUTO was controlling. The system will stay in that mode until the MODE or AUTO switch is pressed. Pressing the MODE button also activates the digital display for the mode selected. If an airflow mode is currently displayed, pressing the MODE button selects the next air flow mode. The air flow direction will sequence through the following modes:

Defog

When the driver selects the MIX-BLEND mode, air delivery is divided between the floor and windshield outlets. The HVAC control module ground the mix-blend mode valve solenoid control circuit. When the solenoid is grounded, vacuum is applied to the mode actuator through the Blue vacuum line, and to the defrost actuator through the Red and the Yellow vacuum lines. The mode actuator will retract, closing the vent door. Applying vacuum to both sides of the defroster actuator will hold the defroster door stationary in the half open position. The heater door will also be held stationary in the half open position through mechanical linkage.

Floor

When the driver selects the FLOOR mode, air is delivered through the floor outlets with some toward the windshield and side vents. The HVAC control module grounds both the lower mode valve solenoid control and the mix-blend mode valve solenoid control circuit. When the solenoids are grounded, vacuum is applied to the mode actuator through the Blue vacuum line, and to the defrost actuator through the Red vacuum line. The mode actuator will retract, closing the vent door. The defroster actuator will retract, closing the defroster door and open the heater door through mechanical linkage.

Bi-Level

When the driver selects the BI-LEVEL mode, cool air is delivered through the instrument panel outlets while warm air is delivered through the floor outlets. The HVAC control module grounds the lower mode valve solenoid control circuit. When the solenoid is grounded, vacuum is applied to the mode actuator through the Brown and the Blue vacuum lines, and to the defrost actuator through the Red vacuum line. Applying vacuum to both sides of the mode actuator will hold the vent door stationary in the half open position. The defroster actuator will retract, closing the defroster door and open the heater door through mechanical linkage.

Panel

When the driver selects the panel mode, air is delivered through the instrument panel outlets and a small amount is delivered to the floor. The HVAC control module grounds the lower mode valve solenoid control and defrost mode valve solenoid control circuit. When the solenoids are grounded, vacuum is applied to the mode actuator through the Brown vacuum line, and to the defrost actuator through the Red vacuum line. The mode actuator will retract, opening the panel door. The defroster actuator will retract, closing the defroster door and open the heater door through mechanical linkage.

Front Defrost

If the HVAC system is in front defrost mode when you turn the vehicle OFF, the HVAC system will restart in front defrost unless the engine is OFF longer than 40 minutes. If the engine is OFF longer than 40 minutes, the system will restart in the previous operating mode set prior to using front defrost, with outside air being drawn into the vehicle.

The front defrost mode is the only setting that is not controlled by the automatic HVAC system. When FRONT DEFROST is selected, the A/C compressor is activated and outside air is brought into the vehicle. The blower motor will be activated and air will be directed toward the windshield with a small amount of air toward the side window outlets. Pressing the AUTO or OFF button will turn OFF front defrost mode. Pressing the FRONT DEFROST button will return the HVAC system to the last operating mode. Recirculation mode is not available in front defrost. The rear window defogger does not affect the HVAC system at all.

The HVAC control module grounds the upper mode valve solenoid control and the mix-blend mode valve solenoid control circuits. When the solenoids are grounded, vacuum is applied to the mode actuator through the Blue vacuum line and to the defrost actuator through the Yellow vacuum line.

Outside Air

When the OUTSIDE AIR switch is pressed, outside air is brought into the vehicle. This mode has no effect on the system when FRONT DEFROST mode is selected. OUTSIDE AIR and RECIRCULATION are separate modes and are not available together. When OUTSIDE AIR is selected, when in automatic mode, the HVAC system will stay in this mode until AUTO is pressed again.

Recirculation

When the recirculation is requested, whether manual or automatic, a solenoid inside the vacuum control assembly connects the recirculation actuator to the vacuum source. Power is provided to the recirculation solenoid by the ignition 3 voltage circuit. Ground is provided by the recirculation valve solenoid control circuit and HVAC control module. When the solenoid is grounded, vacuum is supplied to the recirculation actuator. The recirculation actuator retracts, closing the recirculation door. This draws air from inside the vehicle instead of fresh air from the outside.

Recirculation can be used in both automatic and manual operation. The only time recirculation is not available is when FRONT DEFROST or MIX-BLEND is selected. The RECIRC LED will flash three times to alert the driver that recirculation mode is not available. When in automatic mode, recirculation will stay ON until either the vehicle operator selects OUTSIDE AIR or the automatic system has cooled the vehicle sufficiently.

Automatic

The automatic HVAC system will warm up/cool down and maintain the interior temperature of the vehicle by controlling the A/C compressor clutch, blower motor, air temperature, mode and recirculation actuators to achieve the desired temperature. For fully automatic operation, both the blower and mode switches must be in the AUTO position. Blower speeds will change automatically based on inputs to the HVAC control module. The HVAC control module will always come back to the last settings after an ignition cycle or, if equipped, to the last settings of the driver by pressing the UNLOCK button on the remote keyless entry fob and placing the ignition in RUN.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. To warm the interior quickly, maximum heat is used where the blower is at maximum speed, floor mode, air temperature is in full hot and outside air is being drawn in. The vehicle operator can select the extreme warm setting, but the system will not warm the vehicle any faster. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

In warm temperatures, the automatic HVAC system will provide A/C in the most efficient manner. To cool the interior quickly, full cold is used where the blower is at maximum speed, air temperature actuator is in full cold and the recirculation actuator is drawing air from inside the vehicle. The vehicle operator can select the extreme cool setting, but the system will not cool the vehicle any faster. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.