Is Defogging Done with Hot Air or Cold Air?
3 Answers
Both warm air and cold air can be used for defogging. Here are specific details on whether to use warm or cold air for defogging: 1. In winter, use warm air to defog the front windshield. Warm air defogs more slowly but prevents secondary fogging. 2. In summer, use cold air to defog the front windshield. Cold air defogs faster but may cause secondary fogging. 3. Fogging occurs due to a significant temperature difference between the inside and outside of the car or excessive moisture inside the vehicle. When using the air conditioning for defogging, turn on the external circulation to speed up the process.
In my over 20 years of driving experience, I've found that using hot air is the most reliable way to defog, especially on cold winter mornings. The interior is warm while outside it's cold, and the fogging on the windows is caused by condensation due to the temperature difference. Blowing hot air quickly heats the glass surface, evaporating the water droplets and immediately clearing the view. If you turn on the cold air instead, the glass gets even colder, making the fog worse and reducing visibility. Once, in a hurry, I turned on the cold air and ended up with more and more fog, nearly causing an accident. So now, during winter or rainy seasons, I directly press the hot air defog button, set it to the highest temperature and maximum airflow, and it clears up within two minutes. This also helps prevent moisture buildup on snowy or rainy days, ensuring safer driving. Regularly cleaning the AC filter to avoid dust blocking the vents improves the effect even more. In short, developing good habits can save a lot of hassle.
As an enthusiast who often helps friends with car issues, choosing hot air over cold air for defogging is mainly based on physics. Fogging is essentially condensation of water droplets when warm air meets cold glass. Blowing hot air raises the temperature, speeding up and thoroughly evaporating the moisture. While cold air can reduce the temperature difference, it tends to make the glass colder, causing more condensation, resulting in poor effectiveness and higher fuel consumption. Modern cars' automatic defogging systems combine air conditioning dehumidification with hot air, making it a one-button solution. Remember not to use just natural or cold air, as it slows down the defogging process and compromises safety. I've tested it in my car—hot air cuts defogging time by half compared to cold air. Also, turning up the temperature after pressing the defog button helps restore visibility faster. Regularly check if the air conditioning is functioning properly, as it plays a key role in assisting dehumidification.
