Air Distribution

When the mode switch is turned, a signal is sent from the HVAC control module to the vacuum control assembly. The HVAC control module provides a ground for the necessary mode actuator solenoid. This connects 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.

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 circuit and splice pack. The HVAC control module communicates directly to the Powertrain Control Module (PCM) on the class 2 serial data and ECM/PCM/VCM class 2 serial data circuits through the splice pack.

Mode Switch
Use the MODE switch in order to change the air delivery mode in the vehicle. The air flow direction will sequence through the following modes:
^ VENT
^ BI-LEVEL
^ FLOOR
^ MIX-BLEND
^ FRONT DEFROST

When in AUTO mode, the HVAC control module will deliver air through the following modes:
^ VENT
^ FLOOR
^ BI-LEVEL

Off Mode
Turn the FAN switch to the OFF position 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. Since the A/C compressor is not running, the incoming air may be warmed but not cooled.

Vent Mode
When VENT is selected, air is delivered through the instrument panel outlets with a small amount of air delivered to the floor. 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.

Floor Mode
When Floor is selected, air is delivered to the floor outlets. 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.

Mix-Blend Mode
When Mix-Blend is selected, air is delivered to the windshield outlets and the floor outlets. 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.

Defrost Mode
When Defrost is selected, air is delivered to the windshield outlets. Vacuum is applied to the mode actuator through the Blue vacuum line, and to the defrost actuator through the Yellow vacuum line. The mode actuator will retract, closing the Vent Door. The defroster actuator will retract, opening the Defroster Door and close the Heater Door through mechanical linkage.

Outside Air Mode
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. The outside air LED will not illuminate in automatic mode.

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. The HVAC control module grounds the recirculation mode valve solenoid control circuit. 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 recirculation LED will flash to alert the driver that recirculation mode is not available. The recirculation LED will not illuminate in automatic mode. 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. The recirculation mode has a 10 minute timer. After the timer expires, the HVAC control module will command OUTSIDE AIR. Any time the recirculation button is pressed the A/C compressor clutch automatically engages.