Categories: Modification

【100 Questions】What is the reason why car windows tend to fog up on rainy days? Simple maintenance methods and air conditioner utilization techniques

table of contents
●What causes car windows to fog up when it rains in summer?
●What’s the trick to quickly defogging air conditioners?
●If the glass is not clean, it will easily fog up. It is recommended to clean it regularly.

Why does car windows fog up when it rains in summer?


Has the front windshield or the inside of the car window ever fogged up in summer or winter?

The reason why car windows fog up is because the breath and sweat of the passengers turn into water vapor. These gases mix with the air in the car and exceed the "saturated water vapor amount" and turn into small water droplets (mist).

For example, when there is high temperature and rainfall in summer, the humidity inside and outside the car is quite high. If the air conditioner is not turned on, the temperature and humidity in the car will rise. In addition, the exhaled gas and sweat of the passengers will increase the humidity, and it is easy to exceed the saturated water vapor amount.

In fact, small water droplets adhere to everywhere in the car. They just atomize on the transparent and moisture-impermeable glass surface and become visible to the naked eye.

Tips for quickly defogging air conditioners?


In fact, as long as the air circulates, there will be no fogging. When it is difficult to open the windows, turning on the air conditioner is a common method.

As long as the "AC button" is turned on, the dehumidification function will be activated, and the defogging button can also be turned on.If the car windows are foggy, you can blow the air-conditioning outlet toward the car windows.

You can also change the vehicle air conditioner from "internal circulation" to "external circulation". Although setting it to internal circulation when the air conditioner is on can defogging, introducing outside air can defogging more quickly.

If the glass is not clean, it will easily fog up. It is recommended to clean it regularly.


To keep car window glass from fogging, daily maintenance is also very important. Car window glass will become dirty due to exhaust gas brought into the car from outside, dust and grease from human hands. If you smoke, the smoke components will also adhere to it. Invisible dirt like this will form subtle bumps on the glass, making it easier for water droplets to adhere.

For maintenance, use a damp wiping cloth or glass cleaner to remove dirt first. Commercially available wet wipes for cleaning can also be used. After removing the dirt, you can dry wipe it with a clean cloth. If the detergent remains, this is also the cause of fogging due to the adhesion of water droplets, so you should pay more attention to this.

After dry wiping, you can leave it without any treatment, or you can apply anti-fogging agent or water-repellent coating to prevent fogging.

When washing the car, carefully clean the air intake holes under the windshield to prevent dirt from entering the car. This is also a way to prevent fogging. It is also a good idea to replace the air conditioner filter regularly.

Especially in winter when the temperature difference between the outside air and the interior of the car is large, it is particularly easy to fog up. It is recommended that you clean the glass frequently.

Original source:"The inside windows of your car tend to fog up on rainy days. Could something that is often overlooked be the cause?" Easy maintenance techniques and how to use your air conditioner
Want to see more:MOBY

This post was last modified on December 19, 2023 7:32 am


Dreamer is what I am, but unlike many, I struggle to make my dreams come true. I own, seo, admin and site editor. I am a father, married, Christian, Northeastern/Brazil and Libran. I love cars <3

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