The air delivery description and operation is divided into four areas:

HVAC Control Module

The HVAC control assembly is a non-class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive and ignition 3-voltage circuits provide power to the control assembly. An integrated potentiometer controls air temperature door position. The integrated vacuum system controls the mode door position. The control assembly supports the following features:

The blower motor forces outside air into the vehicle's interior. The vehicle operator determines the blower motor's speed when the driver places the blower switch in one of the following positions:

The blower motor will operate in any switch position other than OFF, as long as the ignition switch is in the RUN position. When the ignition switch is ON, power from the underhood fuse block is delivered to the load side of the blower motor relay through the ignition 3 voltage circuit. Once energized, the load control switch inside the relay connects the HVAC control module to power through the battery positive voltage circuit. The blower motor and mode switches are located within the HVAC control module. The blower motor OFF input is connected in series at the HVAC control module by the off blower motor control circuit.

Power is provided to the blower motor from the instrument panel fuse block. Depending upon selected blower speeds, voltage is either supplied directly to the blower motor or voltage is varied by a series of in-line resistors. Power and ground are provided to the HVAC control module by the battery positive voltage, ignition 3-voltage circuit, ground circuits and splice pack.

Low Blower Speed

When the Low (1) blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the low blower motor control circuit. Voltage is divided between 4 series resistors, the blower motor resistor assembly relay, and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The blower motor resistor assembly provides a ground path for the blower motor.

Medium Blower Speeds

When the Medium 1 (2) blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 1 blower motor control circuit. Voltage is divided between 3 series resistors, the blower motor resistor assembly relay, and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The blower motor resistor assembly provides a ground path for the blower motor.

When the Medium 2 (3) blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 2 blower motor control circuit. Voltage is divided between 2 series resistors, the blower motor resistor assembly relay, and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The blower motor resistor assembly provides a ground path for the blower motor.

When the Medium 3 (4) blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 3 blower motor control circuit. Voltage is divided between a series resistor, the blower motor resistor assembly relay, and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The blower motor resistor assembly provides a ground path for the blower motor.

High Blower Speed

When the High (5) blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly relay through the high blower motor control circuit. The voltage energizes the relay, causing the blower motor to be connected to the battery positive voltage circuit. The blower motor resistor assembly provides a ground path for the blower motor.

Off

When the OFF position is selected, the HVAC control module applies voltage to the blower switch off input within the HVAC control module through the off blower motor control circuit. When the HVAC control module receives this input, any blower and A/C requests will be cancelled and the A/C request LED will turn off. Fresh air will still be brought from the outside, but the LED indicator will not illuminate. The temperature and mode controls will continue to function only to manipulate the fresh air that enters the vehicle. The recirculation function can still be activated. The recirculation mode will stay on until either fresh air is selected. The HVAC control module will stay in recirculation mode for 30 minutes after the ignition switch has been turned off.

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:

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. 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.

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. 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.

Floor

When the driver selects the FLOOR mode, air is delivered through the floor outlets with some toward the windshield and side vents. 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.

Defog

When the driver selects the DEFOG mode, air delivery is divided between the floor and windshield 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 PANEL 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.

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.

When FRONT DEFROST is selected, the A/C compressor is activated and outside air is brought into the vehicle. Air will be directed toward the windshield with a small amount of air toward the side window 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. Recirculation mode is not available in front defrost. The rear window defogger does not affect the HVAC system at all.

Outside Air Mode

When the OUTSIDE AIR switch is toggled, 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.

Recirculation Mode

When the recirculation switch is pressed, a solenoid inside the HVAC control module connects the recirculation vacuum actuator to the vacuum source. Power is provided to the recirculation switch by the ignition 3-voltage circuit. Ground is provided by the ground circuit and splice pack. The recirculation actuator retracts, closing the recirculation door. This brings air from inside the vehicle instead of fresh air from the outside.

Recirculation is available in all modes except FRONT DEFROST and MIX-BLEND. The recirculation mode will stay on and the LED will illuminate until either outside air or a non-recirculation mode is selected. The HVAC control module will stay in recirculation mode for 30 minutes after the ignition switch has been turned off. Recirculation can be selected with the blower motor in either the ON or OFF position.