What to Do When Car Windows Fog Up in Cold Weather?
3 Answers
Press the defogging button, turn on the air conditioning (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 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 reasons 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 are different, the surface with the lower temperature will have a lower saturation 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 dehumidification function to reduce air humidity and remove fog. In summer, especially when multiple people enter the car, if the air conditioning is not turned on promptly, the high humidity from exhaled breath can quickly cause the windshield to fog up. In this case, turn on the air conditioning to blow cold air onto the windshield, using the dehumidification function to remove the fog quickly. If the humidity is too high and the air conditioning is not effective, slightly open a window to rapidly reduce the humidity inside the cabin. Combining this with the air conditioning can speed up the process. Air Conditioning Heating: Use the method of reducing the temperature difference to remove fog. In winter, blowing warm air onto the glass quickly raises the temperature of the front glass, reducing the temperature difference between the inside and outside surfaces of the window, thereby preventing heavy fogging on the windshield. 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. Avoid setting the temperature to the coldest position, as prolonged use may cause the outer surface of the windshield to fog up. Spraying Anti-Fog Agents for Prevention: Spray a small amount of defogging agent onto 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 on the glass and forming fog. This is especially useful in cold winters. Alternatives to defogging agents include dish soap, soapy water, glycerin, alcohol, or saltwater. After applying, let it dry and then wipe off excess residue with chamois or a soft dry cloth. This can 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 of the car, reducing the temperature difference and gradually dissipating the fog. The principle of this method is the same as using cold air from the air conditioning. However, opening windows 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. Turn on the rear window heating switch, and the fog on the rear window will disappear in about a minute.
Fogging on the car windows in cold weather is a common issue. Every time it happens, I simply turn on the air conditioner to the highest heat setting, set the fan speed to maximum, and direct the airflow at the windshield for a few minutes to quickly clear the fog. If the air conditioner has a defogging button (usually marked with a windshield icon), pressing it makes the process even more convenient. When starting the car in cold weather, slightly open the windows by a few centimeters for two to three minutes to allow ventilation between the inside and outside air, balancing the humidity before closing the windows and turning on the air conditioner. Keeping a dry towel in the car to wipe the inside of the windows when parked can help prevent fogging. Fogging mainly occurs because the humid air inside the car condenses on the cold glass, forming water droplets. To avoid this, refrain from bringing wet items into the car or run the heater for a few minutes before parking to dry out the interior, ensuring a safer and more comfortable drive. Regularly cleaning the air conditioner filter can also help.
In winter, when driving causes fogging, I find the simplest method is to use the automatic air conditioning mode—press the AUTO button after getting in the car, set the temperature a bit higher, and it will automatically dehumidify and blow air. If it's cold at first, you can manually adjust the air vents to blow directly at the windshield or open the side windows a bit for ventilation. When the humidity inside the car is too high, it's easy to fog up, so I remind myself not to breathe heavily or drink hot beverages in the car. If the fog is too thick to see clearly, pull over to deal with it instead of wiping the windshield while driving. Buying an anti-fog spray to apply on the glass also works well, and placing a desiccant under the seat can help prevent fogging. Remember, safety comes first—always check your car's condition before heading out.
