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The fog is moisture condensing on the cold windshield surface. Use heat directed at the windshield with AC on. The AC dries out the moisture and the heater warms up the surface preventing additional condensation.
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When I press the defrost button in my car, it turns both the heat and AC on at the same time. I assume this is to remove water from the air with the AC, then warm up the air increasing its capacity to hold water with the heat.
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It’s not about temperature, it’s about condensation and humidity. Turn on the AC regardless of temp (e.g. even if it’s cooler out and you’re blasting the heat) and the defog too.
Source: I fucking live in Seattle and it fucking rains all the time
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If your windows gets foggy you need to turn up the heat as that lowers the relative humidity and direct the air towards the windshield, also check below the floor mats for water. If your car is a swimming pool your windows will be foggy forever.
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Clean your window.
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Trick question:
Dew point is the exact temperature at which the current level of humidity forms. Heat is good because it makes the air at the surface stop condensing. AC is good because it dries the air out forming the condensate in your air box. Cracking the window is generally enough warmth to interrupt the process. Most new cars have a defrost mode that turns on both heat and ac to dry the air out.
So the answer is do anything, except just turning the ac colder.
Always use heat. Anytime you have a fogged up window heat will cause that moisture to evaporate. Cold will always make the window cooler which causes more condensation.
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People in comments assume the heat or air conditioning even work.
Air conditioning also rapidly reduces humidity, so that tends to be the ideal option.
But if neither heat nor air conditioner work, well tough it out and roll the windows down...
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Remember to pull your sun visors down. My AC doesn't stay charged so I have to rely on heat alone to defog windows. The visors trap the warm air.
Temp isn't as important as ac
Every time. And I'm halfway through life. I could do a web search, but who ever thinks of that except when this happens? Will I do a web search now? No. I have other stuff to think about. And so it goes.
Just the other day I was listening to this song by the Grateful Dead:
"Sometimes the light's all shining on me ...
Sometimes I can barely see ...
And lately it appears to me
What a long strange trip it's been. "
crack a window
Atleast you have a car
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Open the window.
Whichever of the AC/Heat is on, just switch it to the other one. Or turn it off. Or open the windows.
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