What to Do When Car Windows Fog Up Inside on Rainy Days?
2 Answers
Press the defogging 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 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 the purpose of defogging. The method of using warm air to defog is the same as using cold air, but it should be noted that warm air should not be used for defogging on rainy days, as it will initially increase the fog. When car windows fog up, turn on the external circulation. The reason for car windows fogging up: 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 and form tiny water droplets, resulting in 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 and the air conditioning is not turned on in time, the humidity from exhaled breath can quickly cause the windshield to fog up. At this time, you can turn on the air conditioning to blow cold air onto the windshield, using the dehumidifying function to remove the fog quickly. However, if the humidity is too high and the air conditioning is not effective enough, you can 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, blowing warm air onto the glass quickly raises the temperature of the windshield, reducing the temperature difference between the inside and outside surfaces of the window, thereby 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 this can cause the outer surface of the windshield to fog up over time. Spraying Anti-Fog Agents 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 is formed, effectively preventing water vapor from condensing on the glass and forming fog, which is especially useful in cold winters. Alternatives to defogging agents include dishwashing liquid, soapy water, glycerin, alcohol, or salt water. After applying, let it dry and then wipe off any excess with a chamois or soft dry cloth. This can keep the car windows fog-free for several days. Opening Windows for Airflow: If the fog inside the car is not too heavy, you can open the windows on both sides to 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. The downside of opening windows for airflow is obvious: it cannot be used in rainy or snowy weather, on highways, or when the fog is heavy. Rear Windshield Heating: Most cars have a rear windshield electric heating function, though the button positions may vary, the function is the same. Turn on the windshield heating switch, and the fog on the rear windshield will disappear in about a minute.
A few days ago, I was driving in heavy rain when the windshield fogged up completely, which was quite frightening. The main reason was the low temperature inside the car, causing moisture from breathing to condense into water droplets on the cold surface. I immediately turned on the air conditioning to defog mode, directing warm air toward the windshield at around 25°C with medium fan speed, while also switching to external circulation to let fresh air in and reduce humidity inside. If conditions allow, cracking the window slightly for a minute or two can help clear the fog quickly. If there's no time, gently wiping the glass with a clean towel or tissue can work, but be careful not to get distracted while driving. Remember, sudden fogging during rain is extremely dangerous as it obstructs visibility of vehicles ahead, increasing the risk of accidents. So, I recommend regularly checking if the defog function works properly and adjusting the settings before it rains for a safer journey.
