For 1990-2009 cars

### Temperature Control Knob

The temperature control knob (1) controls the amount of air flow to the heater core, regulating the temperature of the air entering the vehicle.

When the temperature control knob is moved completely to the coldest position, the air mix door closes in order to block the flow of air to the heater core.

When the temperature control knob is moved completely to the hottest position, the air mix door opens fully in order to allow the air to flow through the heater core.

Moving the temperature control knob between the coldest and the hottest positions allows the driver to adjust the passenger compartment temperature to the most comfortable level.

### Mode Control Knob

The mode control knob (5) allows the driver to route the air into the passenger compartment through different outlets. The mode knob enables the selection of the following modes:

Ventilation: In this position, the air flows from the instrument panel (IP) outlets. The blower speed control lever controls the air quantity. The vehicle speed affects the air quantity if the fresh/recirc lever is in the FRESH position. A higher vehicle speed allows more air into the passenger compartment. Some air is delivered if the blower speed is in the OFF position.
Bi-Level: In this position, the air flows from the IP outlets and from the floor outlets. The air that flows from the floor outlets is warmer than the air that flows from the IP outlets.
Heat: In this position, most of the airflow is from the floor outlets. There is some airflow from the windshield outlets.
Heat and Defrost: In this position, a portion of the heated airflow is from the windshield outlets. The remaining airflow is from the side window outlets and from the floor outlets.
Defrost: In this position, most of the airflow is from the windshield outlets. A small amount of the airflow is from the side window outlets and from the floor outlets.

### Blower Speed Control Knob

The blower speed control knob (3) regulates the amount of air delivered into the passenger compartment. The blower speed control knob has 5 positions: OFF and speeds 1-4. The heater case contains the blower motor. The blower motor is located behind the right side of the IP.

### Fresh/Recirc Lever

The fresh/recirc lever (2) determines whether fresh outside air or recirculated passenger compartment air enters the vehicle's heater and ventilation system.

Moving the fresh/recirc lever to the recirculate position provides the quickest air delivery by closing the blower mode door. Outside air is not delivered to the passenger compartment in this position. Because the vehicle has a full-time outside air system, a small amount of outside air enters the passenger compartment regardless of the mode control position. Recirculate mode is helpful in heating up the passenger compartment faster. However, during normal heater operation use the fresh mode to prevent window fogging.

### Air Conditioning Switch

The A/C switch (4) signals the A/C compressor control module that A/C system operation has been requested. In all of the modes, the A/C switch must be in the ON position in order to engage the compressor. If the A/C switch is in the ON position, the switch sends an A/C system request signal to the A/C compressor control module.

The position of the temperature control lever on the heater control unit controls the A/C output temperature. A cable connects the lever to the airflow door in the heater case. The position of the door controls the airflow through or around the heater core.