Press the defogging button, turn on the air conditioning (A/C) switch, set the temperature to the lowest, and turn on the external circulation to remove fog. Both cold and warm air can defog car windows, but warm air works slower than cold air. The most effective method is to use cold air, which blows dry, cold air directly onto the glass, preventing water vapor from condensing on the glass and achieving defogging. The method for warm air defogging is the same as cold air defogging, but note that warm air should not be used on rainy days as it may initially worsen the fog. Always use external circulation when defogging car windows. The reason for foggy car windows: There is a certain temperature difference between the inside and outside of the car. If the temperatures inside and outside the car are different, the surface with the lower temperature will have a lower saturated vapor pressure than the surrounding environment, causing water vapor to gather on the glass surface in the form of tiny droplets, forming fog. Methods to defog car windows: Air Conditioning Cooling: Use the air conditioning's cooling and dehumidifying function to reduce air humidity and remove fog. In summer, especially when multiple people enter the car without turning on the air conditioning promptly, the exhaled air has high humidity, and the windshield will fog up quickly. At this time, turn on the air conditioning to blow cold air onto the windshield, using the dehumidifying function to remove the fog quickly. If the humidity is too high and the air conditioning is not effective enough, slightly open a window to quickly reduce the humidity inside the car. Combining this with the air conditioning will yield faster results. Air Conditioning Warm Air: Use the method of reducing the temperature difference to remove fog. In winter, blow warm air onto the glass to quickly raise the temperature of the windshield, reducing the temperature difference between the inside and outside surfaces of the glass, thereby preventing heavy fogging. However, note that the rear and side windows heat up more slowly, so it takes longer to remove all the fog. Whether the air conditioning is automatic or manual, turning it on helps with dehumidification. Do not set the air conditioning temperature to the coldest position, as this may cause the outer surface of the windshield to fog up over time. Applying Anti-Fog Spray: Spray a small amount of defogging agent on the car windows and wipe it clean to remove dirt and stains. While polishing the glass, a thin, transparent protective film forms, effectively preventing water vapor from condensing into fog on the glass. This is especially useful in cold winters. Alternatives to anti-fog spray include dish soap, soapy water, glycerin, alcohol, or saline solution. After applying and letting it dry, wipe off any excess with a chamois or soft dry cloth. This will keep the car windows fog-free for several days. Opening Windows for Airflow: If the fog inside the car is not too heavy, opening the windows on both sides can create airflow between the inside and outside of the car, reducing the temperature difference and gradually eliminating the fog. The principle of this method is the same as using cold air from the air conditioning. However, this method has obvious drawbacks and cannot be used during rain, snow, on highways, or when the fog is heavy. Rear Window Heating: Most cars have a rear window heating function, though the button location may vary. Turning on the rear window heating switch will remove the fog in about a minute.
