For 1990-2009 cars

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.

### Air Speed

The blower motor forces outside air into the vehicle's interior. The vehicle operator determines the blower motor's speed by placing the blower switch in one of the following positions: Low, Medium 1, Medium 2 or High. The blower motor will operate in any position other than OFF as long as the ignition switch is in the RUN position. The blower and mode switches are located within the HVAC control unit. The blower motor is housed in the blower case which is located behind the right side of the instrument panel.

The coil side of the heater relay receives ignition voltage through the GAGE fuse when the ignition switch is in the ON position. When the blower switch is in any position other than OFF, the coil of the heater relay is provided a path to ground through the blower switch to G204. The switch side of the heater relay receives battery voltage through the heater fuse at all times. When the ignition switch is in the ON position, the heater relay is energized and provides battery voltage to the blower motor. The blower motor speed is maintained by controlling the voltage potential to the blower motor. This is achieved by increasing or decreasing the resistance within the blower motors ground path.

#### Low Blower Speed

When the Low blower speed is selected, battery voltage is applied to the blower motor via the heater relay supply voltage circuit. Voltage is divided among the blower motor and 3 series resistors 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 path to G203 for the blower motor.

#### Medium Blower Speeds

When the Medium 1 blower speed is selected, battery voltage is applied to the blower motor via the heater relay supply voltage circuit. Voltage is divided among the blower motor and 2 series resistors 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 and the blower switch assembly provide a path to G204 for the blower motor.

When the Medium 2 blower speed is selected, battery voltage is applied to the blower motor via the heater relay supply voltage circuit. Voltage is divided between the blower motor and 1 series resistor 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 and the blower switch assembly provide a path to G204 for the blower motor.

#### High Blower Speed

When the High blower speed is selected, battery voltage is applied to the blower motor via the heater relay supply voltage circuit. The blower motor resistor is removed from the circuit and the blower switch assembly provides a path to G204 for the blower motor.

#### Off Mode

When the OFF position is selected, any A/C request will be cancelled and the A/C request light emitting diode (LED) will turn off. Fresh air will still be brought from the outside and 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 which will bring air from inside the vehicle instead of fresh air from the outside.

### Air Distribution

The HVAC system provides heating, cooling, ventilation, ram air, and windshield defrosting. The blower fan draws outside air from the plenum at the base of the windshield into the heater case. The forward movement of the vehicle forces additional outside air, or ram air, into the heater case. The heater case contains the heater core, the evaporator core and the airflow doors. Within the heater case, doors direct the air flow to the proper ducts and outlets in response to the positions of the temperature and the mode controls. The heated or cooled air is routed through the ducts to the proper outlets for discharge into the passenger compartment. A control assembly in the instrument panel allows the operator to control the blower speed, the mode of operation, the air inlet position, and the temperature of the air coming from the system.

The body ventilation system provides the passenger compartment with fresh, outside air. Air is drawn into the interior of the vehicle from the intake grille within the cowl panel and drawn out through the ventilator outlets in the body rear panels.

#### Temperature Control

The temperature control determines the amount of air flow to the heater core which regulates the temperature of the air entering the passenger compartment. A cable connects the control to the air flow door that is located in the heater case. When the temperature control is moved to the coldest position, the air mix door closes blocking the flow of air to the heater core. When the temperature control is moved to the hottest position, the air mix door opens fully allowing the air to flow through the heater core. Moving the temperature control between the coldest and the hottest positions allows the operator to adjust the passenger compartment temperature to the desired level.

#### Mode Control

The mode control determines the air flow to the desired air outlet. The mode control is mechanically connected by a cable to the mode door. The mode door position determines the air flow to the ventilation, bi-level, heat, heat/defrost, or defrost air outlets. When the heat/defrost or the defrost position is selected, the A/C system is engaged automatically. Each time the heat/defrost or the defrost mode is selected, the recirculate control automatically defaults to the fresh position. The recirculate position can be manually reselected.

#### Recirculation Control

When the recirculation switch is pressed, a signal is sent from the air inlet and rear defogger switch assembly to the air inlet actuator through the recirculation signal circuit. When the air inlet actuator receives the signal, the actuator moves into the recirculation mode. This brings air from inside the vehicle instead of fresh air from the outside. Internal to the actuator are a motor and a circuit board. Polarity to the motor is reversed internally by the circuit board based on the signal from the recirculation switch. Ignition voltage is provided to the actuator through the GAUGE fuse and the ground circuit through junction block 1 at G200. Recirculation is available in any mode but each time the heat/defrost or the defrost position is selected, the recirculate control automatically defaults to the fresh position. The recirculate position can be manually reselected. The recirculation mode will stay on and the LED will illuminate until either outside air or the heat/defrost or the defrost mode is selected. Recirculation can be selected with the blower motor in either the ON or OFF position.

The defogger switch engages the optional rear window defogger grid. An LED within the air inlet and rear defogger switch assembly illuminates when the system is on. The defogger may be shut off manually or, the system will automatically shut off after approximately 15 minutes.