Posted December 20, 2016
Why do car windows fog up when it’s cold outside?
That fog is condensation, or water vapors that rest and collect on your car windows and windshield. Water vapor within the car, even your own breath, can fog up your windows.
When you hold a warm cup of coffee or tea and breathe across the hot liquid, you may see moisture collecting on the edge of the mug. Cover the top of the mug with your hand, and you’ll start to feel moisture. The water vapor from your beverage is condensing on the surface of your hand.
Condensation happens when water vapors change from air to liquid. Temperature differences speed up this process. When the hot water vapor reaches a colder surface, it begins to change state and becomes liquid.
The same thing happens inside your car. Water vapors in the air inside your car and in the air you exhale are relatively warm compared to the outside temperatures. Especially if you have the heater in your vehicle running, the temperature inside the car is much warmer than the temperature outside.
When the warm air hits the cold windshield, the water vapor starts to turn to liquid, leaving a wet fog on your windshield.
Defrosters in your vehicle blow warm dry air to clear the condensation from your windows.
Which is why it’s so important to have your defroster and heater checked this winter. If it is broken or can’t keep up with the fog on the windshield, it can be a safety hazard. You’ll be stuck wiping away the moisture every few minutes in order to see – very distracting and dangerous!
If your defroster is broken, open a window. Bringing in the cold outside air can help equalize the temperature and clear the fog.
Then drive to AM-PM Automotive Repair in White Bear Lake to have your car’s heating system inspected. Our experienced technicians will diagnose the issue that’s preventing the defroster from working and recommend the best maintenance or repair service. Our goal is to help you understand the condition of your vehicle and keep you safe (and warm) on the winter roads.