BMW 320i uses mechanical buttons for its central control. The defogging and heating functions can be directly activated through the buttons. 1. The defogging button includes the front windshield and the rear windshield. Press the corresponding button to open the defogging function of the windshield. 2. To warm the air, turn the knob to the high-temperature zone and adjust the air to start delivering hot air. When the air is turned on, the air conditioning button should be turned off. No intervention is required when the compressor delivers hot air. The air is heated and regulated by the engine coolant and the heat of the glass heating wire. 3. The AUTO function helps the owner to automatically control the temperature inside the car. The air conditioning system determines whether to increase or decrease the air volume based on the sensor signal, and at this time, refrigeration/heating actions should be taken. 4. The recirculation of air refers to the closed-loop circulation of the air in the car, while the external circulation refers to the exchange and displacement of the air inside and outside the car. When there is traffic congestion, tunnels, and other external air quality does not meet the standards, the internal circulation should be selected. When using the internal circulation for a long time, it should not exceed 1 minute and then switch to the external circulation to prevent the impact of air quality on health (except for severe external environments). 5. When the temperature zone synchronization function is turned on, changing the driver's seat temperature will also change the temperature in other zones. In addition, after turning off this function, each zone can independently adjust the temperature, which is more user-friendly.