What to Do When Car Windows Fog Up on Rainy Days?

[DeKendra]

Press the defogging button, turn on the air conditioning cooling (A/C) switch, set the temperature to the lowest, and switch to external circulation to defog. Both cold and warm air can be used to 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 warm air defogging is similar to cold air, 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 car window fogging: There is a temperature difference between the inside and outside of the car. If the temperatures differ, the side with the lower temperature will have a surface saturated vapor pressure lower than the surrounding environment's vapor pressure, causing water vapor to gather on the glass surface in tiny droplets, forming fog. Methods to defog car windows: Air Conditioning Cooling: Use the air conditioning's dehumidification function to reduce air humidity and remove fog. In summer, especially when multiple people enter the car without turning on the air conditioning, the exhaled humid air can quickly fog up the windshield. Turn on the air conditioning to blow cold air onto the windshield, using the dehumidification function to remove fog quickly. If the humidity is too high and the air conditioning is ineffective, slightly open a window to rapidly reduce cabin humidity. Combining this with air conditioning can speed up the process. Air Conditioning Warm Air: Reduce the temperature difference to remove fog. In winter, blowing warm air onto the windshield quickly raises its temperature, reducing the temperature difference between the inside and outside surfaces and preventing heavy fogging. Note that the rear and side windows heat up more slowly, so it takes longer to remove fog completely. Whether using automatic or manual air conditioning, turning it on helps with dehumidification. Avoid setting the temperature to the coldest position, as prolonged use can cause fogging on the outer surface of the windshield. Applying Anti-Fog Spray: Spray a small amount of defogging agent on the car windows and wipe it clean to remove dirt and stains. This forms a thin transparent protective film that prevents water vapor from condensing into fog, especially useful in cold winters. Alternatives to anti-fog spray 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 windows fog-free for several days. Opening Windows for Airflow: If the fog is light, open the side windows to create airflow between the inside and outside of the car, reducing the temperature difference and gradually eliminating fog. This method works similarly to using cold air from the air conditioning. However, it has obvious drawbacks and cannot be used in rain, snow, on highways, or when fog is heavy. Rear Window Heating: Most cars have a rear window heating function, with varying button locations but the same purpose. Turn on the rear defroster, and the fog will disappear in about a minute.