Every driver knows how maddening it is to enter a car on a cold winter morning only to see frost all over the inside of the windshield and windows. How did that happen? More importantly, is there a way to prevent it? The answer is yes.
In really cold temperatures, the heating system works to warm up your car, but at the same time there's humidity coming from your breath and the melting snow under your boots. Later, when you get out of the vehicle, said humidity will stick to the windows and form a thin but frustrating layer of frost that you'll have to scrape the next morning.
To prevent this from happening, you have to let the hot air and humidity out the car, for example by cracking a window open minutes before you arrive at your destination. Turning the AC on also does the trick.
You're welcome!
Source: Meteomedia