Air Distribution

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
The MODE switch is labeled Air Flow on the HVAC control module. 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:
^ VENT
^ BI-LEVEL
^ MIX-BLEND
^ FLOOR

Off Mode
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.

Mix-Blend Mode
When the driver selects the MIX-BLEND mode, the MODE switch is adjusted until WINDSHIELD and MID are displayed. 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 Mode
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 Mode
When the driver selects the BI-LEVEL mode, the MODE switch is adjusted until MID and FLOOR are displayed. In this mode, air is delivered through the instrument panel and 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.

Vent Mode
When the driver selects the VENT mode, the MODE switch is adjusted until MID is displayed. 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 Vent Door. The defroster actuator will retract, closing the Defroster Door and open the Heater Door through mechanical linkage.

Front Defrost Mode
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 Mode
When the RECIRC switch is toggled OFF, 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 mode is selected in automatic mode, the HVAC system will stay in this mode until AUTO is pressed again.

Recirculation Mode
When the recirculation mode 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 mode 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.

The recirculation mode 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 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.

Dual Zone Control Switch
The right air temperature switch is provided to allow the passenger to offset air discharge temperatures on the right side of the vehicle. Passenger temperatures can be set 3°C (6°F) cooler or warmer than the primary setting. To activate the dual zone, the passenger turns the right air temperature switch to the desired offset. Temperature offset will be allowed as long as the set temperature is not in maximum hot or cold settings.

The instrument panel fuse block provides power to the right air temperature actuator through the ignition 3 voltage circuit. Ground is provided by the HVAC control module and ground circuit.

The right air temperature actuator is an electronic stepper motor with feedback potentiometers. 0 volts drives the actuator in one direction while 5 volts moves the actuator in the opposite direction. When the actuator receives 2.5 volts, actuator rotation stops. A 5 volt reference signal is sent out over the 5 volt reference circuit, from the HVAC control module, to the right air temperature actuator. When a desired temperature is selected, whether manual or automatic, the solid state circuit is used to determine the right air temperature door position signals value. A separate 5 volt reference is sent from the HVAC control module to the solid state circuit. The HVAC control module software uses this reference voltage to determine the right air temperature actuators position through the right air temperature door control circuit. The motor moves the right air temperature door to the desired position. Ground for the right air temperature actuator are provided by the low reference circuit and HVAC control module.