How to Solve Windshield Fogging?
3 Answers
Press the defogging button, turn on the air conditioning (A/C) switch, set the temperature to the lowest, and turn on the external circulation to remove fog. 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 of using warm air to defog is the same as using cold air, but it's important to note that warm air should not be used for defogging on rainy days as it may initially worsen the fogging. Always use external circulation when defogging car windows. 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 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 in tiny droplets, forming 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 promptly, the exhaled air has high humidity, and the windshield will fog up quickly. In this case, 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 enough, slightly open the window to rapidly reduce the humidity inside the cabin. 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 glass, preventing 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. Avoid setting the temperature to the coldest position, as prolonged defrosting may cause fogging on the outer surface of the windshield. Applying 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 is formed, effectively preventing water vapor from condensing into fog. This is especially useful in cold winters. Alternatives to anti-fog agents include dish soap, soapy water, glycerin, alcohol, or saline solution. After applying, let it dry and then wipe off any excess with a chamois or soft dry cloth. This will keep the windows fog-free for several days. Opening Windows for Airflow: If the fog inside the car is not too heavy, open both 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 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 will disappear in about a minute.
I've been driving for ten years and often encounter windshield fogging, especially on rainy days or in winter. You can immediately use the air conditioning's defogging mode, set the fan speed to the highest, and blow cold air on the glass for a few seconds—it works quickly. If there's no defogging button, crack the window slightly to allow air circulation; once humidity drops, the fog will dissipate. Avoid wiping the glass by hand while driving, as it can easily lead to accidents. I recommend keeping the interior dry after parking, placing some dehumidifying bags, or opening the doors for ventilation on sunny days. Clean the glass with a dedicated cleaner once a week to prevent oil buildup from worsening fogging. Check if the air filter is clogged—if dirty, it can reduce defogging efficiency. In winter when using the heater, first blow cold air to clear the fog before adjusting the temperature to avoid worsening the fog. These small habits can make your driving experience safer.
As a driver who frequently transports family members, windshield fogging is a significant issue. Turning on the air conditioning immediately upon entering the car often causes fogging, so I habitually press the defogging switch or windshield heating button right away. In summer when humidity is high, cold air is effective for dehumidification; in winter, first use low temperature to disperse the fog, then gradually increase the warmth. Avoid placing wet clothes or rain gear inside the car, and develop the habit of turning on the air conditioning for one or two minutes before driving to pre-defog. If the fogging is severe, safely pull over to deal with it rather than taking risks. Anti-fog sprays are quite useful, with one application lasting several days. Keep the air conditioning ducts clear to prevent leaves and dust from blocking the vents. Safety comes first—turn on hazard lights and drive slowly when visibility is poor. For prevention, use the external air circulation more often to reduce moisture buildup.
