What to Do When the Car's Exterior Glass Fogs Up?

[LeGabriella]

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 car glass, 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 may initially worsen the fog. When the car glass fogs up, external circulation should be turned on. The reason for car glass 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 side 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 glass: 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 high humidity of exhaled air can quickly cause the windshield to fog up. At this time, turn on the air conditioning to blow cold air onto the windshield, using the dehumidifying function of the air conditioning to quickly remove the fog. If the humidity is too high and the air conditioning is not effective, slightly opening a window can quickly reduce the humidity inside the car. Of course, combining this with the air conditioning can achieve 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 can quickly raise the temperature of the windshield, reducing the temperature difference between the inside and outside surfaces of the glass and preventing excessive fogging. However, it should be noted that the rear and side glass temperatures rise 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 of the air conditioning should not be set to the coldest position, as this may 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 onto the car glass and wipe it clean to remove dirt and stains. While cleaning the glass, a thin transparent protective film is formed on the glass, effectively preventing water vapor from condensing and forming fog, especially suitable for cold winters. Alternatives to anti-fog agents include dishwashing liquid, soapy water, glycerol, alcohol, or salt water. After applying and letting it dry, wipe off excess residue with chamois or a soft dry cloth to ensure the car glass remains fog-free for several days. Opening Windows for Airflow: If the fog inside the car is not heavy, opening the side windows can create airflow 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 airflow is very obvious: it cannot be used in rainy or snowy weather, on highways, or when the fog is heavy.

[GriffinFitz]

I find that when the car's exterior glass fogs up, it's usually caused by temperature differences, such as the car's interior being too warm from the heater on a cold day, leading to condensation on the outside of the glass. My first step is to turn on the windshield wipers to remove most of the fog, which works quickly. Then, I adjust the air conditioning system, directing the airflow to the front windshield and using moderately warm air for a few minutes to clear the fog. If that doesn't work, I manually wipe the glass with a soft cloth or spray some defogger. As part of my routine, I make it a habit to clean the glass surface before winter to reduce dirt buildup and prevent moisture condensation. These small tricks have saved me a lot of trouble, especially during the rainy season or early morning drives, ensuring my visibility isn't compromised. Remember not to rinse with cold water directly, as it can worsen fogging. Sticking to simple steps helps maintain safe driving.