Why Does Frost Form on Car Windows in Winter?
4 Answers
The reasons for frost forming on car windows in winter are as follows: 1. The primary cause of frost inside the car during winter is the temperature difference between the interior and exterior of the vehicle. 2. Because the temperature inside the cabin is higher than outside, the car windows come into contact with the colder external environment, causing the moisture inside the cabin to condense on the inner windshield, forming frost. When the moisture in the warm air approaches the cold glass, it cools down and condenses into frost. Frost typically forms in winter or during cold mornings and evenings. Here are some solutions to prevent frost on car windows in winter: 1. Start the engine and wait for a while. If you notice frost on the car windows, you can first start the engine and let it warm up for a bit. 2. Turn on the fan and adjust it to the warm air setting. After starting the car engine, you can turn on the fan, set it to warm air, and adjust the fan position to direct airflow toward the front windshield.
I used to be bothered by this when I first started driving. It's mainly because the car is warm inside and cold outside in winter, especially when you breathe, which creates a lot of moisture in the car. The warm moisture hits the cold windshield and quickly turns into frost or fog. This is especially true when you first start the car and turn on the heater, making it more prone to fogging or frosting. So, for the first few minutes before driving, I turn up the heater to blow air onto the windshield to expel the moisture from the car. Alternatively, I might crack the window to let in some dry, cold air. If you have a garage, leaving the car door open for a while before parking at night to air out the interior moisture helps a lot. Most importantly, don’t breathe directly onto the glass, or all the defrosting efforts will be in vain.
This is actually quite a physical phenomenon. Human breathing and sweating inside the car increase air humidity. When the temperature of the car windows falls below the dew point of the air, water vapor condenses into frost. My experience is to fully open all doors and windows for ventilation for one minute after parking, allowing the temperature and humidity inside and outside the car to equalize before locking the car. The next morning, the windows will be much cleaner. If frost does form, never use hot water to wash it off—the drastic temperature difference can crack the glass. Instead, gently scrape it with a hard plastic scraper or turn on the car and blast the windshield with maximum air flow. Driving with frost on the windshield is very dangerous, so make sure it's completely cleared before you start driving.
I used to hate this when driving the old Santana. Later, I learned the principle of air conditioning dehumidification: set the heater to windshield mode and turn on the AC compressor. Although it consumes a bit more fuel, the effect is quick. The AC removes moisture, while the warm air heats the windshield, combining both methods to clear fog rapidly. Nowadays, most new cars come with a quick defog button—just press it, and the AC and fan speed adjust automatically. Once, I saw someone scraping frost with a bank card, which left many scratches. If you must use a coin temporarily, wrapping its edge with a soft cloth makes it safer. Fogging up is no small matter; not being able to see the road is extremely dangerous.
