The air delivery controls are divided into two primary areas. The first, air speed, is dependent upon blower motor speed. The second, air distribution, is related to various single or multiple air outlets.

The HVAC control module is a non-class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and air distribution settings. The ignition 3 and battery positive voltage circuits provide power to the control module. The control modules supports the following features:

The HVAC control assembly applies voltage to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:

When the operator requests High speed, the HVAC control assembly applies voltage to the blower motor relay through the high blower motor control circuit. The voltage energizes the blower motor relay, connecting the blower motor to battery positive voltage.

Low Blower Speed

When the Low blower speed is selected, the HVAC control module applies voltage to the blower motor resistors through the low blower motor control circuit. Voltage is decreased across 4 series resistors to achieve the desired blower speed. The blower motor is grounded through the blower motor resistor assembly and ground circuit of the blower motor resistor assembly.

Medium Blower Speeds

When the Medium 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistors through the medium 1 blower motor control circuit. Voltage is decreased across 3 series resistors to achieve the desired blower speed. The blower motor is grounded through the blower motor resistor assembly and ground circuit of the blower motor resistor assembly.

When the Medium 2 blower speed is selected, the HVAC control module applies voltage to the blower motor resistors through the medium 2 blower motor control circuit. Voltage is decreased across 2 series resistors to achieve the desired blower speed. The blower motor is grounded through the blower motor resistor assembly and ground circuit of the blower motor resistor assembly.

When the Medium 3 blower speed is selected, the HVAC control module applies voltage to the blower motor resistors through the medium 3 blower motor control circuit. Voltage is decreased across a resistor to achieve the desired blower speed. The blower motor is grounded through the blower motor resistor assembly and ground circuit of the blower motor resistor assembly.

High Blower Speed

When the High blower speed is selected, the HVAC control module applies voltage to the blower motor relay through the high blower motor control circuit. The blower motor relay is internal to the blower motor resistor assembly. The voltage energizes the blower motor relay, causing the blower motor to be connected to the battery positive voltage circuit. The blower motor is grounded through the blower motor resistor assembly and ground circuit of the blower motor resistor assembly.

Off Mode

When the OFF position is selected, the HVAC control module applies voltage to the off blower motor control within the HVAC control module through the off blower motor control circuit. When the HVAC control module receives this input, any A/C request will be cancelled and the A/C request LED will turn off. Fresh air will still be brought in from the outside.

Mode Switch

The mode switch is a rotary vacuum valve that directly applies vacuum to the appropriate vacuum actuator. Use the mode switch to change the air delivery mode in the vehicle.

Vent Mode

When the driver selects the VENT 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 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, 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 Mode

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 Mode

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 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.

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.

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.

Recirculation is only available in MAX. When MAX mode is selected, vacuum is applied to the recirculation actuator. The force of the vacuum overcomes the spring pressure of the spring inside the actuator. This moves the actuator, which is linked to the recirculation door, into recirculation mode. This brings air from inside the vehicle instead of fresh air from the outside.