Why does the car windshield frost on the outside when the air conditioning is on in summer?
2 Answers
In summer, the car windshield frosts on the outside because the hot air outside the window meets the cold air inside the car, causing the glass to frost. Here are some methods to defog the car windows: 1. Spray anti-fog agent: Spray a small amount of defogging agent on the car window and wipe it clean to remove dirt and stains on the glass. While polishing the glass, a thin transparent protective film is formed on the glass, which can effectively prevent the formation of fog caused by condensation of water vapor on the glass. 2. Air conditioning cooling: Use the air conditioning's cooling and dehumidification function to reduce air humidity and remove fog. In summer, especially when many people enter the car and do not turn on the air conditioning in time, the humidity of the exhaled air is high, and the front windshield will quickly fog up. At this time, you can turn on the air conditioning to blow cold air towards the front windshield, using the air conditioning's dehumidification function, and the fog on the front windshield can be removed quickly.
Having driven for so many years, it's quite common to see frost forming on the outside of the windshield when using air conditioning in summer. The main reason is setting the car's AC temperature too low, with cold air blowing directly onto the glass, causing the outer surface temperature to drop significantly. When warm, humid outside air hits this cold glass surface, moisture quickly condenses into tiny droplets, appearing like frost. This physical principle is essentially the same as water droplets forming on the outside of an ice-cold soda bottle. The solution is simple: I recommend adjusting the AC temperature to around 24°C, or redirecting the vents downward to avoid direct airflow onto the glass. Using external air circulation can also help balance the temperature difference. If condensation has already formed, simply using the wipers or keeping a bottle of automotive glass anti-fog spray handy works wonders. Don't prioritize cooling comfort over visibility – summer driving safety comes first.
