How to De-Fog your Windshield in 3 easy steps!
Auto Airheads Unite!
One of the more frequent questions I get from women about their cars is, “How do I de-fog my windshield?” Auto airhead Patrice has been there. I was driving home from work after a gloomy, rainy day when all my car windows began to fog up. Suddenly I’m in a desperate situation, and I start to panic. I can’t see out the windshield, the wipers aren’t removing the fog, and I’m fumbling around with the Air and Temperature controls. A foggy windshield is a pretty obvious safety issue, so it’s an ominous sign few people know how to remove fog.
Luxury and Limited Cars Save the Day!
Luxury or limited-model cars automatically defog your windshield. They have electronic control buttons you can push to activate the heating, A/C, and defrost system. As an added safety measure, when you turn on the defrost in these cars, the electronic controls will also turn ON the A/C system and turn OFF the recirculation button, removing fog from the windshield. With the exception of the temperature, don’t touch or change any controls once you turn on the defrost button.
If you have a car with knobs and hand controls, you must activate the controls yourself to de-fog your windshield.
Inside or Outside Fog?
First, determine if the fog is on the inside or outside of your windshield. A quick hit of the wipers will readily tell you if the fog is inside or outside. Outside fog will clear after a sweep of the wipers. Inside fog, will not. In an outside fog situation, you’ll continue to use your wipers, so make sure they are in good condition. Inside fog requires a few more steps to remove, but it is not hard!
How to quickly remove inside fog from your windshield.
Turn your air control to defrost and your fan speed to a high setting.
Turn your temperature control to hot and turn ON the A/C.
Turn OFF the recirculation button and crack the windows.
A - Fan Speed B - Recirculation button C - Temperature
D - A/C button E - Air Control
Voila! Sit back and watch as the fog quickly “melts” away from your windshield!
Ok, I know you’ve got questions.
Questions like:
What causes the difference in fog inside and outside the windshield?
Why does turning on the A/C with the defrost work to defog?
But what if it is cold out? I don’t want to turn on the A/C!
Many people don’t understand how to remove fog from the windshield because it involves scientific terminology, like condensation, and a few variable conditions, like temperature gradients and climate, that alter the rules on how to remove fog. It doesn’t appear to be a straightforward task or easy to learn, so we dismiss it.
Essential maintenance and use of our car shouldn’t be a mystery, and it shouldn’t make us feel dumb. You can defog a windshield without getting PTSD from 11th-grade science. This applies to winter, summer, rain, or hail.
Let’s start by breaking down how the defrost works on your car.
The defrost is named, quite literally, after its function to remove frost from the windshield. It also removes fog from the windshield. Your vehicle’s heating and a/c system gathers outdoor air and blows it into your car and onto your windshield at a chosen temperature and speed. When your air controller is set to the defroster, outdoor air blows on the windshield. If the outside of your windshield is frosted with ice and you turn on the defroster, air with melt the frost away. If the outside or the inside of the windshield is covered in fog, air may not melt away the fog.
If recirculation is activated, it takes air from inside your vehicle and recirculates it through the heating and a/c system to blow back into your car. This is great to save on money when using your A/C in the summer.
What causes the difference in fog inside and outside the windshield?
Fog is a cloud of wet air (vapor) that will deposit as a thick layer on your car’s windshield. Fog deposits inside, on the windshield, because the car's inside temperature is warmer than the outside temperature, and there is moisture in the inside air. Many things like temperature, climate, and human breathing can cause the car’s inside air to be warmer and more humid than the outside air.
Why does turning on the A/C with the defrost work to defog?
When you use the A/C system in your car, any outdoor air blown inside the car will have the moisture removed by something called an evaporator. The evaporator is a key component in the A/C system to give you cold air in the hot summer, but it also works as a dehumidifier.
If you have fog on the inside of your car windshield and turn the defroster on with no A/C, you could be blowing more fog or wet air onto the windshield, worsening the situation. If you want to remove inside fog from your windshield, the A/C must run and work correctly. The dry air will blow inside the car and on the windshield versus humid air with no A/C.
But what if it is cold out? I don’t want to turn on the A/C!
Running the A/C on a warm setting will help defog your windshield faster however, you can use the A/C at any temperature setting. You don’t need to have the temperature set to cold to use the A/C. Check out this video that explains more.
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A do-it-herself guide to auto maintenance, roadside emergencies, and the real scoop on how women can get honest car service at the garage, from engineer turned auto mechanic and award-winning entrepreneur Patrice Banks. SIGNED BY PATRICE.