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 only operate if the blower switch is 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 blower motor relay receives ignition voltage through the DEF fuse when the ignition switch is in the ON position, and is permanently grounded at G201. The switch side of the blower motor relay receives battery voltage through the HTR and blower fuses at all times. When the ignition switch is in the ON position, the blower motor relay is energized and provides battery voltage to the blower motor. When the blower switch is in any position except OFF, a ground path is provided to the blower motor at G201 through the blower motor resistor (except in HIGH) and the closed contacts of the blower switch.

On vehicles equipped with A/C, when the blower switch is in any position except OFF, a signal is provided to the powertrain control module (PCM) for idle control.

#### Low Blower Speed

When the Low blower speed is selected, battery voltage is applied to the blower motor via the blower motor relay supply voltage circuit. Voltage is divided between 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 and the blower switch assembly provide a pathway to ground 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 blower motor relay supply voltage circuit. Voltage is divided between 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 pathway to ground for the blower motor.

When the Medium 2 blower speed is selected, battery voltage is applied to the blower motor via the blower motor 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 pathway to ground for the blower motor.

#### High Blower Speed

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

#### Off Mode

When the OFF position is selected, any A/C request will be cancelled and the A/C request 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 mode 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 (if equipped) 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 position 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 lever 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 lever is mechanically connected by a cable to the mode door in the heater case. 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, a mechanical linkage on the heater case closes an electrical switch which engages the A/C system.

Air quantity is controlled by the blower switch. Air quantity is also affected by vehicle speed when the fresh/recirculation lever is in the FRESH position. The passenger compartment receives more air as the vehicle speed increases. The passenger compartment receives some air even if the blower switch is in the OFF position.

#### Recirculation Control

The fresh/recirculation control lever determines whether fresh outside air or recirculated passenger compartment air enters the vehicle's heater and ventilation system. A cable connects the control lever to the air inlet door that is located in the blower case. The recirculate position provides the quickest air delivery and is helpful in heating up the passenger compartment faster. Because the vehicle is equipped with a full-time outside air system, a small amount of outside air enters the passenger compartment regardless of control position. During normal heater operation use the fresh mode in order to prevent window fogging.