Should You Use Cold or Hot Air to Defog Car Windows on Rainy Days?
3 Answers
Using cold air is more effective because when the temperature outside the car is higher or lower than inside, moisture forms on the windows. You can also avoid using the air conditioning by opening the windows, which will make the fog disappear as well. Hot air can also dry the fog, but it is not as effective as cold air. Here are the correct methods to remove fog from car windows: 1. Using air conditioning cold air to defog: The most effective way to remove fog from windows is to turn on the air conditioning (A/C) in cooling mode, activate the external circulation, and direct the airflow towards the windshield at maximum speed. The dry cold air will blow directly onto the windshield, creating a 'gas film' on the surface that prevents water vapor from condensing on the glass. The fog will disappear in less than a minute. 2. Using warm air to defog: The method is the same as using cold air, except you direct warm air towards the glass instead of cold air. This essentially dries the water vapor, eliminating concerns about fog reappearing. However, warm air defogging is slower than cold air, and the fog may initially become thicker when you first turn it on. You'll need to wait patiently for a few minutes.
Right after it rains, the inside of the windows is particularly prone to fogging up. I usually deal with it by using the cold air setting. Press the defog button on the AC (the one with the fan-shaped symbol), turn on the AC cooling, set the fan to maximum, and direct it at the windshield—the fog clears up in half a minute. However, using cold air can make you feel freezing, so it's more suitable for short trips or emergencies. You can also use hot air, but you'll need to wait for the engine's water temperature to rise and endure a few minutes of increased fogging before it clears. Before every trip, I spray anti-fogging agent, which works effectively for several days. Avoid leaving damp towels in the car, and put umbrellas in plastic bags before placing them in the trunk, otherwise the humidity will cause fogging in no time.
Last time I encountered a heavy rainstorm, I couldn't see the dashboard clearly. I tried using hot air, but it only made things blurrier and I almost rear-ended someone. Since then, I prioritize using cold air by turning the knob to the blue zone and turning on the external circulation. Once the AC compressor kicks in, the windshield clears up instantly. When it's cold, you can use warm air, but remember to crack the window slightly to speed up moisture removal—close it only after the fog clears. Installing a hygrometer in the car is quite practical; if humidity exceeds 70%, turn on the AC to dehumidify—no need to even wipe the glass. Of course, don’t forget to replace the AC filter on time—if it's clogged, no amount of airflow will help.
