Press the defog button, turn on the air conditioning (A/C) switch, set the temperature to the lowest, and switch to external air circulation to remove fog. Both cold and warm air can defog car windows, but warm air is slower than cold air. The most effective method is using 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 using warm air is the same as cold air, but note that warm air should not be used for defogging on rainy days as it can initially worsen the fog. Always use external air circulation when defogging car windows. The reason for car window fogging: There is a temperature difference between the inside and outside of the car. If the temperatures inside and outside the car differ, the side with the lower temperature will have a surface water saturation vapor pressure lower than the surrounding environment's vapor pressure, causing water vapor to gather on the glass surface, forming tiny water droplets that create 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, quickly causing the windshield to fog up. In this case, turn on the air conditioning to blow cold air onto the windshield, using the dehumidifying function to remove fog quickly. If the humidity is too high and the air conditioning is ineffective, slightly open the windows to rapidly reduce the cabin's humidity. Combining this with the air conditioning can speed up the process. Air Conditioning Warm Air: Use warm air to reduce the temperature difference and remove fog. In winter, blowing warm air onto the glass quickly raises the windshield's temperature, reducing the temperature difference between the inner and outer surfaces and preventing excessive fogging. However, 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. Avoid setting the temperature to the coldest position, as prolonged use can cause the outer windshield to fog up. Applying Anti-Fog Spray for Prevention: 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, especially useful in cold winters. Alternatives to defogging agents include dish soap, soapy water, glycerin, alcohol, or saline solution. After drying, wipe off excess residue with chamois or a soft dry cloth to keep the windows fog-free for several days. Opening Windows for Airflow: If the fog inside the car is not heavy, open the side windows to create airflow between the inside and outside, reducing the temperature difference and gradually dissipating the fog. This method works on the same principle as using cold air from the air conditioning. However, opening windows has obvious drawbacks and is not suitable during rain, snow, highways, or heavy fog. Rear Windshield Heating: Most cars have a rear windshield heating function, though the button location may vary. Turn on the heating switch, and the fog on the rear windshield will disappear in about a minute.
