The Air Delivery description and operation is divided into 5 areas:

HVAC Control Module

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

Blower Motor Control Processor

The blower motor control processor is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive voltage and ground circuits enable the control processor to operate. The HVAC control module provides a PWM signal to the control processor in order to command the blower motor speed. The processor supplies 12 volts to the blower motor through the blower motor voltage supply circuit. The control processor uses the blower motor ground as a low side control to adjust the blower motor speed.

The blower motor forces air to circulate within the vehicle's interior. The vehicle operator determines the blower motor's speed by placing the blower motor switch in a desired speed position or by selecting automatic operation. The blower motor will only operate if the blower motor switch is in any position other than OFF, and the ignition switch is in the RUN position. In manual operation, once a blower speed is selected, the blower speed remains constant until a new speed is selected. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature.

As the requested blower speed increases, the following conditions occur:

As the requested blower speed decreases, the following conditions occur:

Purge Operation

If the ambient air temperature is less than 2°C (35°F) and the coolant temperature is less than 10°C (50°F), then a 75-second purge will occur. The purge will begin as soon as the coolant temperature reaches 4°C (40°F). The mode door will move to the defrost position and the blower motor will be near half speed.

The operator uses the mode switch on the HVAC control module to change the air delivery mode in the vehicle. The HVAC control module communicates the mode door position to the vacuum control assembly through 5 solenoid control circuits.

Vent Mode

When the operator selects VENT, the mode actuator has vacuum applied to it through the brown vacuum line, making the vent door open.

Bi-Level Mode

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

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 red 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:

When the operator presses the Recirculation switch, a solenoid inside the vacuum control assembly connects the recirculation door vacuum actuator to the vacuum source. The recirculation actuator retracts, closing the recirculation door. The recirculation operation can function with blower motor in either the ON or OFF position. Recirculation will continue and the LED will illuminate until either outside air is selected or the next ignition cycle. Recirculation is not available in Defrost and Mix-Blend mode.

In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and recirculation.

To place the HVAC system in Automatic mode, the following is required:

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature: