What to Do When Car Windows Fog Up in the Rain?
2 Answers
Press the defog button, turn on the air conditioning (A/C) switch, set the temperature to the lowest, and switch to external circulation to defog. Both cold and warm air can 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 and achieving defogging. The method for warm air defogging is the same as cold air, but note that warm air should not be used on rainy days as it may initially worsen the fog. Always use external circulation when defogging car windows. The reason for car window fogging: There is a temperature difference between the inside and outside of the car. If the temperatures differ, the side with the lower temperature will have a lower saturated vapor pressure on its surface compared to the surrounding environment, causing water vapor to gather on the glass surface and form tiny droplets, resulting in fog. Methods to defog car windows: Air Conditioning Cooling: Use the air conditioning's dehumidification 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 exhaled humid air can quickly cause the windshield to fog up. In this case, turn on the air conditioning to blow cold air onto the windshield, utilizing its dehumidification function to remove fog quickly. If the humidity is too high and the air conditioning is ineffective, slightly open a window to rapidly reduce cabin humidity. Combining this with the air conditioning can speed up the process. Air Conditioning Heating: Use the method of reducing the temperature difference to remove fog. In winter, blowing warm air onto the glass quickly raises the windshield's temperature, reducing the temperature difference between the inside and outside surfaces, thereby preventing heavy fogging. However, note that the rear and side windows heat up more slowly, so it takes longer to fully defog them. Whether using automatic or manual air conditioning, turning it on aids dehumidification. Avoid setting the temperature to the coldest, as prolonged use can cause frost on the outer windshield. Applying Anti-Fog Spray or Other Preventatives: Spray a small amount of defogging agent on the car windows and wipe it clean to remove dirt and stains. This also forms a thin transparent protective film that effectively prevents water vapor from condensing on the glass, especially useful in cold winters. Alternatives to defogging agents include dish soap, soapy water, glycerin, alcohol, or saline solution. After applying and letting it dry, wipe off excess residue with a chamois or soft dry cloth to keep windows fog-free for several days. Opening Windows for Airflow: If the fog is light, open both side windows to create airflow between the inside and outside of the car, reducing the temperature difference and gradually eliminating the fog. This method works on the same principle as using cold air from the air conditioning. However, it has obvious drawbacks and cannot be used during rain, snow, on highways, or when fog is heavy. Rear Window Heating: Most cars come with a rear window heating function, though the button location may vary. Turn on the rear defroster, and the fog will disappear in about a minute.
I've been driving for over ten years, and nothing scares me more than foggy windows during rainy days. When this happens, I immediately switch the air conditioning to defog mode and direct it at the windshield with the fan at maximum speed for the best effect. If the AC isn't powerful enough, I crack the window slightly to allow air circulation, which helps the fog dissipate faster. When heavy rain makes it hard to see the road, I slow down, turn on the hazard lights to avoid rear-end collisions, and find a safe spot to pull over before continuing. Fogging mainly occurs due to temperature differences and humidity condensation between the inside and outside of the car, so using the external air circulation to keep the air dry can prevent it. I recommend regularly checking if the AC system is working properly, cleaning the windows before it rains, and avoiding leaving wet items in the car to reduce the risk of fogging.
