The air delivery description and operation is divided into six 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. Two integrated potentiometers control air temperature door position and blower motor speed. The integrated vacuum system controls the mode door position. The control assembly 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.

Auxiliary heat or A/C has a blower motor that is independent to that system. Voltage is supplied to the auxiliary heater switch or auxiliary A/C switch from the A/C relay in the underhood fuse block. Either the auxiliary heater blower motor switch and/or the auxiliary A/C blower motor switch applies voltage to the auxiliary 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 auxiliary blower motor per particular speed request:

When the operator requests High speed, voltage is applied directly to the auxiliary blower motor.

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.

MAX A/C

When the operator selects MAX A/C, the mode actuator has vacuum applied to it through the Yellow vacuum line, making the vent door open. The defrost actuator has vacuum applied to it through the Green vacuum line, making the defrost door close and the heater door open through mechanical linkage. A solenoid inside the HVAC control assembly connects the recirculation door vacuum actuator to the vacuum source. The recirculation actuator retracts, allowing air to be recirculated. A/C is forced ON.

A/C

When the operator selects A/C, the mode actuator has vacuum applied to it through the Yellow vacuum line, making the vent door open. The defrost actuator has vacuum applied to it through the Green vacuum line, making the defrost door close and the heater door open through mechanical linkage. A/C is forced ON.

Bi-Level Mode

When the operator selects Bi-Level, the following occurs:

Vent Mode

When the operator selects VENT, the mode actuator has vacuum applied to it through the Yellow vacuum line, making the vent door open. The defrost actuator has vacuum applied to it through the Green vacuum line, making the defrost door close and the heater door open through mechanical linkage.

Floor Mode

When the operator selects FLOOR, the mode actuator has vacuum applied to it through the Brown vacuum line, pushing the vent door closed. The defrost actuator has vacuum applied to it through the Green vacuum line, pulling the defrost door closed and opening the heater door through mechanical linkage.

Mix-Blend Mode

When the operator selects Mix-Blend, the following occurs:

Defrost Mode

When the operator selects Defrost, the following occurs:

There are no mode adjustments for the auxiliary system.

recirculation is only available in MAX A/C. When MAX A/C is selected a solenoid inside the HVAC control assembly connects the recirculation door vacuum actuator to the vacuum source. The recirculation actuator retracts, closing the recirculation door.