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TWeaKoR t1_j0m5qza wrote

Reply to comment by [deleted] in How does high humidity affect perceived temperature in hot and cold environments? by MindTheReddit

It's also why you should use air con when blowing hot air to demist your windows in your car. The air con cools the air, which lowers the humidity and condenses out some of the moisture, then heating it up leaves air with relatively lower humidity. This is because the air's capacity to hold water goes up with temperature, so if you have the same amount of water in cool air as hot, the hot will feel drier.

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iowamechanic30 t1_j0mqux2 wrote

This is done automatically in almost all cars on the road today and vintage cars aren't set up to work like that so don't turn the ac on to defrost your windows.

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TWeaKoR t1_j0n0iu3 wrote

It's done automatically in cars when you set it to the window clear settings, for the most part, and more and more cars have proper climate controls, but that isn't always the case.

Regardless, the reason it automatically turns AC on is because it clears the mist. If you have AC off and find you're getting misting on the windows, putting AC on will probably clear it, even when it isn't blowing on the front windshield it should lower the relative humidity in the cabin. Yes, it will use a tiny bit more electrical power from the engine, but it serves a purpose.

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iowamechanic30 t1_j0ojm98 wrote

I don't think we're on the same page. There are people that will read this post and turn their heat off and turn the ac on to defrost their windshield. I am trying to prevent that, when you turn the defroster on the car automatically engages the ac to dry the air out but also blows hot air. Just let the car do its thing.

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