How to Deal with Foggy Car Windows on Rainy Days?
4 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. Foggy car windows can be cleared with either cold or warm air, 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 should be noted that warm air should not be used for defogging on rainy days, as it will initially increase the fog. When the car windows fog up, the external circulation should be turned on. The reason for foggy car windows: 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 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 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 of the exhaled air is high, and the windshield will quickly fog up. At this time, you can turn on the air conditioning to blow cold air onto the windshield, using the air conditioning's dehumidifying function to remove the fog on the windshield 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 cabin. Of course, you can also use it in combination with the air conditioning for faster results. Air Conditioning Warm Air: Use the method of reducing the temperature difference to remove fog. In winter, use warm air to blow hot air onto the glass, quickly raising the temperature of the front glass and reducing the temperature difference between the inner and outer surfaces of the window glass, which can prevent excessive fogging on the windshield in time. However, it should be noted that the rear and side windows heat up slowly, so it takes longer to remove all the fog. Whether the air conditioning is automatic or manual, turning it on helps with dehumidification; the air conditioning temperature control should not be set to the coldest position, otherwise, the outer surface of the windshield may fog up after prolonged use. 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 from the glass. While polishing the glass, a thin transparent protective film is formed on the glass, which can effectively prevent water vapor from condensing on the glass and forming fog, especially suitable for cold winters. Alternatives to anti-fog agents include dishwashing liquid, soapy water, glycerin, alcohol, or salt water. After drying, use chamois or a soft dry cloth to wipe off any excess fibers, which can ensure the car windows remain fog-free for several days. Opening Windows for Airflow: If the fog inside the car is not 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 allowing the fog to slowly disappear. The principle of this method is the same as using cold air from the air conditioning. The downside of opening windows for airflow is very obvious: it cannot be used in rainy or snowy weather, on highways, or when the fog is heavy. Rear Window Heating: Most cars have a rear window electric heating function, although the button positions may vary, the function is the same. Turn on the window heating switch, and the fog on the rear window will disappear in about a minute.
Yesterday, while driving my kid to cram school, I encountered heavy rain, and the windshield fogged up instantly. I quickly pressed the defrost button with the fan-shaped icon, and the air conditioning automatically adjusted to maximum airflow directed at the glass, clearing it up in half a minute. Nowadays, many cars come with heated side mirrors, so remember to also turn on that rectangular button. If the fog keeps reappearing, it’s likely because the recirculation mode is on—switch to fresh air mode to introduce dry air. Once, while driving my wife to work, I noticed the side windows fogging up, so I simply adjusted the air vents to blow directly at them, which is much safer than wiping by hand. On rainy days, it’s best to check the cabin air filter beforehand—if it’s clogged, the defrosting effect will be compromised. Keeping a chamois cloth in the car is also useful; a quick wipe during traffic jams is super convenient.
With twenty years of taxi driving experience, I've encountered this issue the most. Start the vehicle and turn on the AC directly, set the temperature to the lowest, and adjust the fan speed to above the third level—cold air defogs much faster than warm air. Remember to turn off the recirculation mode to let fresh air in, otherwise, the moisture from breathing will fog up the glass again immediately. For side window fogging, there's a trick: angle the air vents completely toward the glass for clearer visibility than adjusting the rearview mirror. Keep a bottle of anti-fog spray and wipe the inner windows with a dry cloth treated with it—this reduces fogging frequency by half. If it's raining heavily, applying a mix of dish soap and water to the windows in advance works well too, similar to the anti-fog principle of swimming goggles.
Last time my neighbor asked me about this, I taught her the simplest three-step method: start the engine first when it rains, then turn on the AC, press the fan-shaped defog button, and finally switch to the external air circulation. She tried it and said it was much easier than using a cloth. Many cars now come with an ECON mode for the air conditioning; activating it makes the compressor work intermittently, saving fuel while maintaining the defogging effect. If the rear window fogs up, just press the rear defroster button—the one with the heating wire pattern. Once, while dropping my kid off at school, I casually used an anti-fog wipe for glasses on the window and found it could also work in a pinch.
