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 blower motor forces outside air into the vehicle's interior. The vehicle operator determines the blower motor's speed by toggling the blower motor switch manually or by using the automatic mode.

The blower control module receives power from the fuse block through the battery positive voltage circuit. Ground is provided by the blower control module through the ground circuit.

When any blower speed is selected, whether manual or automatic, a pulse width modulated (PWM) signal is sent from the heater and A/C control to the blower control module through the blower speed circuit. When a low blower speed is requested, the PWM signal is reduced. When a higher blower speed is requested, the PWM signal is increased. A 4 to 12 volt signal is then sent to the blower motor from the blower control module through the motor positive circuit. A signal is delivered back to the heater and A/C control, from the blower control module, through the blower speed feedback circuit to let the heater and A/C control know what speed the blower motor is in. The blower motor is grounded through the motor negative circuit. An open circuit, short to ground or short to battery on the blower speed circuit will disrupt the PWM signal and cause the blower motor to not operate. In automatic operation, the heater and A/C control will determine what blower speed is necessary in order to achieve or maintain a desired temperature. Toggling the blower switch manually also activates the VF display for the blower speed selected.

When the recirculation switch is pressed, a signal is sent from the heater and A/C control to the recirculation vacuum solenoid valve, through the vacuum solenoid valve control circuit. Power is supplied to the recirculation vacuum solenoid valve through the battery positive power supply circuit. When the recirculation vacuum solenoid valve is grounded, vacuum is applied to the recirculation actuator. The recirculation valve allows air from the passenger compartment to be recirculated through the HVAC module.

When outside air mode is selected, the recirculation actuator is vented to normal air pressure and the recirculation valve completely closes off the entrance for inside air.

Recirculation is helpful when you are trying to cool the air quickly or trying to limit odors from entering the vehicle. When the system is in the AUTO mode, the system automatically selects recirculation to cool the vehicle's temperature. The recirculation mode will not operate in the front defrost mode, as to prevent windshield and window fogging due to moisture in the vehicle.

When manually selected, recirculation will stay on until either the vehicle operator selects outside air, by pressing the recirculation switch, or the heater and A/C control automatically moves the recirculation actuator. When selected, the recirculation icon will illuminate on the VF display. Recirculation is available in all modes except front defrost.

The automatic HVAC system will warm up/cool down and maintain the interior temperature of the vehicle by controlling the A/C compressor clutch, blower motor, air temperature, mode and recirculation actuators to achieve the desired temperature. For fully automatic operation, depress the left temperature knob. Blower speeds will change automatically based on inputs to the heater and A/C control.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. On cold engine start-up, low blower speed will be selected and airflow will be directed on the windshield. This is done to prevent windshield fogging. To warm the interior quickly, maximum heat mode is used where the blower is at maximum speed, floor mode, air temperature actuator is in full hot and outside air is being drawn in. The vehicle operator can select the extreme warm setting of 32°C (90°F), but the system will not warm the vehicle any faster or regulate the blower speed. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the heater and A/C control.

In warm temperatures, the automatic HVAC system will provide A/C in the most efficient manner. To cool the interior quickly, maximum cool mode is used where the blower is at maximum speed, air temperature actuator is in full cold and the recirculation actuator is drawing air from inside the vehicle. The vehicle operator can select the extreme cool setting of 16°C (60°F), but the system will not cool the vehicle any faster or regulate the blower speed. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

There are three mode actuators to control the different modes, defrost valve actuator, inside air valve actuator and mode valve actuator. When the mode switch is toggled, a signal is sent from the heater and A/C control to the different actuators through the control circuits. When the actuators receive the signals, they move into the desired positions.

The defroster valve actuator is a DC stepper motor by design. The stepper motor has four field windings that are controlled by the heater and A/C control. When the heater and A/C control needs to move the stepper motor, it energizes the proper field windings which rotates the armature a fixed amount in the proper direction. This fixed amount is called a step. Battery voltage for the stepper motor is supplied by the heater and A/C control when the ignition is in the ON position, through the battery positive power supply circuit.

The inside air valve actuator is a DC stepper motor by design. The stepper motor has four field windings that are controlled by the heater and A/C control. When the heater and A/C control needs to move the stepper motor, it energizes the proper field windings which rotates the armature a fixed amount in the proper direction. This fixed amount is called a step. Battery voltage for the stepper motor is supplied by the heater and A/C control when the ignition is in the ON position, through the battery positive power supply circuit.

The mode valve actuator is a DC stepper motor by design. The stepper motor has four field windings that are controlled by the heater and A/C control. When the heater and A/C control needs to move the stepper motor, it energizes the proper field windings which rotates the armature a fixed amount in the proper direction. This fixed amount is called a step. Battery voltage for the stepper motor is supplied by the heater and A/C control when the ignition is in the ON position, through the battery positive power supply circuit.

Attached to the stepper motors are small gears. When the stepper motors are installed on the HVAC module, they mesh with a larger gears which is part of an assembly that drives the linkage of the air mix doors.

Off Mode

When the vehicle is moving, air flowing over the vehicle increases the air pressure just ahead of the windshield. This forces air into the outside air inlet, into the HVAC module and out through the floor outlets. Since the A/C compressor is not running, the incoming air may be warmed but not cooled. Recirculation can be selected when the heater and A/C control is in the OFF position. The ambient air temperature will show on the display at all times. The heater and A/C control will return to the previous driver settings.

Recirculation Mode

When the recirculation switch is pressed, a signal is sent from the heater and A/C control to the recirculation vacuum solenoid valve, through the vacuum solenoid valve control circuit. Power is supplied to the recirculation vacuum solenoid valve through the battery positive power supply circuit. When the recirculation vacuum solenoid valve is grounded, vacuum is applied to the recirculation actuator. The recirculation valve allows air from the passenger compartment to be recirculated through the HVAC module.

When outside air mode is selected, the recirculation actuator is vented to normal air pressure and the recirculation valve completely closes off the entrance for inside air.

Recirculation is helpful when you are trying to cool the air quickly or trying to limit odors from entering the vehicle. When the system is in the AUTO mode, the system automatically selects recirculation to cool the vehicle's temperature. The recirculation mode will not operate in the front defrost mode, as to prevent windshield and window fogging due to moisture in the vehicle.

When manually selected, recirculation will stay on until either the vehicle operator selects outside air, by pressing the recirculation switch, or the HVAC control module automatically moves the recirculation actuator. When selected, the recirculation icon will illuminate on the VF display. Recirculation is available in all modes except front defrost.

Front Defrost Mode

The front defrost mode is the only setting that is not controlled by the automatic HVAC system. When defrost is selected, by the vehicle operator, the A/C compressor is activated and outside air is brought into the vehicle. The blower motor will be activated on high speed, regardless of coolant temperature and air will be directed toward the windshield and side windows with a small amount towards the floor. Recirculation mode is not available in front defrost. The rear window defogger does not affect the HVAC system at all.

Mode Switch

Use the MODE switch in order to change the air delivery mode in the vehicle. Selection of the MODE switch when in AUTO mode will lock in the air flow mode that AUTO was controlling. The system will stay in that mode until the MODE or AUTO switch is pressed. Toggling the MODE button also activates the VF display for the mode selected. If an airflow mode is currently displayed, pressing the MODE button selects the next air flow mode. The air flow direction will sequence through the following modes: