Why Do Car Windows Get Foggy?
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Respiration
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In many cases, car windows become fogged up due to respiring passengers. When the water vapor in breath comes into contact with the cooler glass of the car window, it turns back into a liquid and collects (condenses). If this is the only cause of condensation, the fogging can be wiped off with a cloth or the windows can be rolled down. If it continues to be a problem, it may be necessary for safe vision to keep the windows rolled down.
Weather and Exterior Fogging
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Differences in temperature between the cabin of the car and the outside are another common cause of fogging windows. If humid, hot air contacts the surface of the window from the outside, water vapor may condense. This causes the window to fog up from the outside. The wipers and rear defroster can be used to take care of condensation on the windshields; rolling down the windows will improve conditions on windows.
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Weather and Interior Fogging
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If the air inside the cabin of the car is warmer than the air outside the car, water vapor may collect on the interior of the windows. In this case, venting the air may help, but it may also be necessary to run both the heater and the air conditioner. The air conditioner takes the humidity out of the interior air; the heater will evaporate the condensation that's already present.
Systemic Problems
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If you experience repeated, otherwise unexplainable fogging of your car windows, there might be a larger problem--such as leaking of gases from the dash or of coolant from the radiator. Maintaining clean windows is a good first step in correcting the problem, but if the issue persists, seek the guidance of a professional.
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