How to Deal with Foggy Car Windshield on Rainy Days?
3 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. Both cold and warm air can be used to defog the car windshield, 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 increase fogging. When the car windshield fogs up, turn on the external circulation. The reason 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 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 fogging. Methods to defog the car windshield: Air Conditioning Cooling: Use the dehumidification function of the air conditioning system 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 and blow cold air onto the windshield. Using the dehumidification function of the air conditioning system, the fog on the windshield can be removed quickly. However, if the humidity is too high and the air conditioning is not effective enough, slightly opening the windows can quickly reduce the humidity inside the car. Of course, 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, 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, thereby preventing excessive fogging. However, it should be noted that the rear and side windows heat up 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 fogging on the outer surface of the windshield over time. Applying Anti-Fog Spray or Other Preventive Measures: 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, which effectively prevents water vapor from condensing on the glass and forming fog. This is especially suitable for cold winters. Alternatives to anti-fog spray include dish soap, soapy water, glycerin, alcohol, or salt water. After applying and letting it dry, use a chamois or soft dry cloth to remove excess residue. This can keep the car windows fog-free for several days. Opening Windows for Air Circulation: If the fog inside the car is not too heavy, you can open the windows on both sides to create air circulation 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 for air circulation is obvious—it cannot be used during rain, snow, on highways, or when the fog is too heavy. Rear Window Heating: Most cars have a rear window heating function, although the button positions may vary, the function is the same. Turn on the rear window heating switch, and the fog on the rear window will disappear in about a minute.
Fogging on the car's front windshield is quite common on rainy days, and I deal with it immediately to avoid obstructing my driving view. Most cars have a dedicated defogging button with an icon resembling a fan-shaped airflow. Pressing it automatically adjusts the air conditioning to external circulation mode, quickly clearing the fog. If the car interior is too humid, cracking the windows slightly to allow air circulation can help remove moisture, but be careful not to let rain in. Using warm air directed at the windshield is effective, but avoid using the highest fan speed to prevent uneven heating of the glass. Regularly wiping the inside of the windshield during maintenance helps prevent oil film buildup, reducing the likelihood of fogging. Safety first—if the fog is heavy, pull over to clean it properly before continuing to drive.
When driving in rainy weather with fogged-up windows, I usually use the air conditioning to solve the problem. After starting the car, I press the defrost button, and the AC switches to cooling mode to dehumidify, clearing the fog in just a few minutes. When there are more people in the car, I turn on the fan to help with air circulation or adjust the temperature control knob to direct airflow toward the windshield. Opening the window slightly can also help by allowing hot and cold air to mix and dissipate the fog. Remember not to wipe the glass with a wet cloth, as it will make the fog worse. For prevention, I regularly clean the glass to keep it clear, and in summer or high-humidity rainy days, I use an anti-fog spray—it works great. This method is simple and convenient.
