What to Do When the Car Windows Fog Up?

[OTanner]

Press the defog button, turn on the air conditioning cooling (A/C) switch, set the temperature to the lowest, and turn on the external circulation to defog. You can use either cold or warm air to defog the 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 the purpose of defogging. The method of using warm air to defog is the same as using cold air, but it is important to note that warm air should not be used for defogging on rainy days, as it may initially worsen the fogging. When the car windows fog up, turn on the external circulation. The reason for car window fogging: 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 of the lower-temperature side will have a lower saturated vapor pressure than the surrounding environment, causing water vapor to gather on the glass surface and form tiny water droplets, resulting in 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 and the air conditioning is not turned on in time, the humidity from exhaled breath can quickly cause the windshield to fog up. In this case, turn on the air conditioning and blow cold air onto the windshield. The dehumidification function of the air conditioning will quickly remove the fog. However, if the humidity is too high and the air conditioning is not effective, slightly open a window to quickly reduce the humidity inside the car. Of course, 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 windshield to quickly raise its temperature and reduce the temperature difference between the inside and outside surfaces of the window, preventing excessive fogging. However, it should be noted that the rear and side windows heat up more slowly, so it takes longer to completely remove the fog. Whether the air conditioning is automatic or manual, turning it on helps with dehumidification. The temperature control should not be set to the coldest position, as prolonged defrosting can cause the outer surface of the windshield to fog up. Applying anti-fog spray or other preventive measures: 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 is formed, effectively preventing water vapor from condensing on the glass and forming fog, which is especially useful in cold winters. Alternatives to anti-fog spray include dish soap, soapy water, glycerin, alcohol, or salt water. After drying, wipe off any excess residue with a chamois or soft dry cloth. This can keep the car windows fog-free for several days. Opening windows for air circulation: If the fog inside the car is not too heavy, you can open the windows on both sides to create air circulation 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. The downside of opening windows for air circulation is very obvious—it cannot be used during rain, snow, on highways, or when the fog is heavy. Rear window heating: Most cars have a rear window electric heating function, although the button location may vary, the function is the same. Turn on the rear window heating switch, and the fog on the rear window will disappear in about a minute.

[AlanaAnn]

I've encountered foggy car windows countless times while driving. First, don't panic. Start the engine and immediately turn on the AC cold air, setting it to high speed and directing it at the windshield to quickly remove moisture and defog. If it's cold outside, switching to warm air for defogging after the engine warms up also works well. Additionally, turning on the external air circulation to let fresh air in helps the fog dissipate quickly. I've found that keeping the windows clean is crucial—oil films or dirt buildup make fogging more likely, so I clean my windows monthly with professional anti-fog spray, which works much better. In winter, it's best to preheat for a few minutes before turning on the heater to avoid sudden fogging due to large temperature differences. Safety first—if the fogging is severe, pull over before dealing with it, and never wipe the windows while driving. Regular maintenance of the AC system, including checking the filter to prevent moisture buildup, is also important.