How to Deal with Foggy Car Windshield?
4 Answers
Press the defog button, turn on the air conditioning (A/C) switch, set the temperature to the lowest, and turn on the external circulation to defog. Both cold and warm air can be used to defog the car windshield, but warm air works 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 may initially increase fogging. When the car windshield fogs up, external circulation should be turned on. The reasons for car windshield 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 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 fogging. Methods to defog the car windshield: 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 without turning on the air conditioning promptly, the high humidity of exhaled air can quickly cause the windshield to fog up. At this point, turn on the air conditioning to blow cold air onto the windshield, using the dehumidifying function to remove the fog quickly. If the humidity is too high and the air conditioning is not effective, slightly open the windows to quickly reduce the humidity inside the car. Combining this with the air conditioning can speed up the process. Air Conditioning Warm Air: Use the method of reducing the temperature difference to remove fog. In winter, blow warm air onto the glass to quickly raise the temperature of the windshield, reducing the temperature difference between the inside and outside surfaces of the glass, which can prevent excessive fogging. However, it should be noted 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. The temperature control should not be set to the coldest position, as this can cause frost to form on the outside of the windshield over time. Applying 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 into fog, especially suitable for cold winters. Alternatives to defogging agents include dishwashing liquid, soapy water, glycerin, alcohol, or saltwater. After drying, use chamois or a soft dry cloth to wipe off any excess fibers, ensuring the car windows remain fog-free for several days. Opening Windows for Airflow: If the fog inside the car is not too heavy, open the side windows 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. However, the downside of opening windows is obvious—it cannot be used during rain, snow, on highways, or when the fog is heavy. Rear Windshield Heating: Most cars have a rear windshield heating function, though the button location may vary. Turning on the windshield heating switch will usually clear the fog on the rear windshield in about a minute.
The most annoying thing while driving is fogging on the windshield. I usually turn on both the air conditioning and windshield defogger mode, and the fog clears up in two to three minutes. In summer, I use cold air, and in winter, warm air—both work fine. For faster results, I blast the maximum airflow, but if the wind noise is too loud, I can always lower it after the fog clears. Some cars have an electric heating defogger button, which is a game-changer—it works in seconds. Recently, I noticed that replacing the air filter makes defogging much quicker, probably because the old filter was too damp. If the fog isn’t too heavy, using warm air in foot and windshield mode is quite comfortable.
Last week, while driving my child to school in heavy fog, the windshield wipers started to create a white haze. I tried turning on the external air circulation first and then increasing the fan speed. Cold air cleared the fog much faster than warm air, but it felt uncomfortably chilly! Temporarily using tissues to wipe the windshield only made it blurrier. An emergency defogging spray worked wonders with just a couple of sprays. Now I've developed a habit: wiping the inside of the glass with a towel before getting in the car and leaving a small gap in the window when parked. By the way, I noticed that turning off the music during defogging allows me to hear the air conditioner's dehumidification sound earlier—once it kicks in, I know the fog is about to clear.
Isn't fogging just caused by temperature difference? Turning on the AC for dehumidification plus directing airflow to the windshield is the quickest solution. Older cars require manual adjustment of the air circulation mode, while newer cars just need a press of the defog button. Winter heating defogs slower but is more comfortable, remember to use external air circulation. Keeping a bottle of anti-fog spray is practical, one application lasts three to four days. Last time, the washer fluid tank leaked unnoticed, and spraying water while wiping the fog made it worse – this detail needs attention. If all else fails, open the window for a few seconds to allow air exchange, but don't try this on the highway.
