Which Button to Press to Clear Windshield Fog?

[StAutumn]

Press the defog button, turn on the air conditioning (A/C) switch, set the temperature to the lowest, and activate the external circulation to defog. You can use either cold or warm air to remove fog from the 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 on the surface and achieving defogging. The warm air method works similarly, but note that using warm air on rainy days 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 has a lower saturated vapor pressure, 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 dehumidification function to reduce air humidity and remove fog. In summer, especially when multiple people enter the car without turning on the AC, the exhaled humid air can quickly cause the windshield to fog up. In this case, turn on the AC to blow cold air onto the windshield, using its dehumidification function to quickly remove fog. If the humidity is too high and the AC is ineffective, slightly open the windows to rapidly reduce cabin humidity. Combining this with the AC can speed up the process. Air Conditioning (Heating): Use warm air to reduce the temperature difference and prevent fogging. In winter, blowing warm air onto the windshield quickly raises its temperature, minimizing the temperature difference between the inside and outside surfaces and preventing heavy fogging. However, the rear and side windows heat up more slowly, requiring more time to fully defog. Whether using automatic or manual AC, turning it on helps with dehumidification. Avoid setting the temperature to the coldest, as prolonged use may cause frost or fog on the outer windshield. Anti-Fog Spray or Alternatives: Spray a small amount of defogging agent onto the car windows and wipe it clean to remove dirt and stains. This creates a thin, transparent protective film that prevents water vapor from condensing into fog, especially useful in cold winters. Alternatives to defogging agents include dish soap, soapy water, glycerin, alcohol, or saline solution. After applying, let it dry and wipe off excess residue with a chamois or soft cloth, ensuring fog-free windows for several days. Window Ventilation: If the fog is light, opening both side windows allows air to circulate, reducing the temperature difference and gradually eliminating fog. This method works similarly to using cold air from the AC. However, it has clear drawbacks—it's not suitable during rain, snow, on highways, or when fog is heavy.