Which Button to Press to Clear Windshield Fog?

[McJoy]

Press the defogging button, turn on the air conditioning (A/C) switch, set the temperature to the lowest, and activate the external circulation to clear the 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 using cold air, which blows dry cold air directly onto the glass, preventing water vapor from condensing and achieving defogging. The method for using warm air 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 surface water vapor pressure lower than the surrounding environment, causing water vapor to gather on the glass surface, forming tiny droplets and creating 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. Turning on the AC to blow cold air onto the windshield and using the dehumidification function can quickly clear the fog. If the humidity is too high and the AC is ineffective, slightly opening the windows can rapidly reduce cabin humidity. Combining both methods yields faster results. Air Conditioning Heating: Use warm air to reduce the temperature difference and remove fog. In winter, blowing warm air onto the glass quickly raises its temperature, reducing the temperature difference between the inside and outside surfaces and preventing heavy fogging. Note that the rear and side windows heat up slower, so it takes longer to clear all fog. Whether using automatic or manual AC, turning it on helps with dehumidification. Avoid setting the AC to the coldest temperature to prevent fogging on the outside of the windshield over time. Applying Anti-Fog Spray: Spray a small amount of defogging agent on the car windows and wipe it clean to remove dirt and stains. This leaves a thin transparent protective film that prevents water vapor from condensing into fog, especially useful in cold winters. Alternatives to anti-fog spray include dish soap, soapy water, glycerin, alcohol, or saltwater. After drying, wipe off excess residue with chamois or a soft dry cloth to keep windows fog-free for several days. Opening Windows for Airflow: If the fog is light, opening both windows can create airflow between the inside and outside of the car, reducing the temperature difference and slowly dissipating the fog. This method works similarly to using cold air from the AC. However, it has clear drawbacks and is unusable during rain, snow, on highways, or when fog is heavy. Rear Window Heating: Most cars have a rear window heating function, though the button location may vary. Turning on the rear defroster clears fog in about a minute.