Why is there frost inside the car windshield?
3 Answers
The reason for frost inside the car windshield: After leaving the car, residual heat inside the vehicle keeps the glass temperature higher than the outside. If the external temperature is too low or it's snowing, the snowflakes landing on the glass will melt initially. As the interior temperature gradually drops to match the outside temperature, the melted snow on the glass begins to freeze. Once frozen, any additional snowflakes won't melt, and the moisture on the glass solidifies into ice beads, forming frost on the glass. Solutions: 1. Warm up the car sufficiently to allow the engine coolant temperature to rise; 2. Once the engine coolant temperature rises, turn on the heater and set it to blow upward toward the windshield to quickly increase the front windshield temperature; 3. When the heater melts the external frost, gently wipe the frost with a car cleaning cloth to accelerate the melting process; 4. After all the external frost has melted, use the windshield wipers to remove any water stains from the glass surface.
I encountered this situation this morning while driving, where the breath inside the car turned into frost and completely covered the front windshield. It's mainly due to the significant temperature difference between the inside and outside of the car—cold outside and warm inside. The moisture from breathing and damp clothes froze on the glass. For a quick fix, you can turn on the air conditioning, set the temperature to the highest, crank up the fan to maximum, and press the defrost button. If you're in a hurry to drive, using a bank card to scrape off the frost works quite well, just be careful not to scratch the glass. To prevent this, avoid leaving wet clothes or open drinks in the car, open the windows after parking to let out the moisture, and always use the external air circulation when running the AC to expel the damp air.
Has anyone noticed that frost on the windshield in cold weather is mostly an interior issue? I’ve experienced this firsthand with older cars without automatic climate control—it’s mainly due to excessive moisture in the AC evaporator. It’s advisable to regularly check the cabin air filter; a clogged one traps humidity inside. A helpful habit: turn off the AC 5 minutes before parking but keep the blower running to dry out the system, saving significant defrosting time later. Applying anti-fog treatment on the glass also works wonders, lasting about two weeks per application. Recently, I’ve kept a moisture absorber pack in the car to combat condensation—it’s surprisingly effective!
