Why You Might Need A Mechanic If Your Windshield Is Always Foggy

Foggy windows on a car aren't an unusual occurrence, especially if you live somewhere very cold or very muggy. When it's cold out, the moist, warmer air inside your car sticks to the inside of the windshield and turns to condensation. If it's very hot and humid, the same thing happens in reverse – hot air from outside is cooled by your car's air conditioning, again turning to condensation. Normally, this can be easily dealt with by using the defogger setting on your AC, alongside some basic upkeep like cleaning your windows.

However, in certain circumstances, the fog on your windows may seem much more persistent than usual, taking longer to remove even with the defogger and immediately returning the moment you stop using it. While it's generally unlikely that this is indicative of a mechanical problem, the possibility is definitely there, which means you might want to book an appointment at your local auto shop. If the matter is left alone for too long, not only will you have to deal with endlessly foggy windows, but your car may be in danger of mechanical failure.

What causes persistent fogging?

The concerning circumstance is when your windshield immediately fogs back up the moment you turn your AC system off, no matter how long you've been driving. In an especially serious situation, your windshield may even remain firmly foggy no matter how long you've had the air running. If you're experiencing this, there are a couple of potential mechanical causes that could warrant a repair appointment.

First, there could be a crack or leak somewhere in your car, either in the body or one of the windows. Even a small crack, if deep enough, can let air of an opposing temperature into your car. As opposing air continues to flow in, the temperature in the cabin will never equalize, which means your windshield will keep fogging. Besides this general annoyance, having hot and cold air flowing through this crack could cause your car's body to expand or contract in a potentially dangerous way.

The other potential cause is a problem with your air conditioning compressor. Whether you're using a dedicated defogging setting or are just circulating warm air, if your compressor's on the fritz, it won't be able to propel the air far enough to actually reach your windshield. Besides the foggy inconvenience, this could be a sign of a looming AC system failure and should be checked out as soon as possible.