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I think every car has re-circulator functionality in AC control panel. But I don't really use it, because it fogs up all of the windows. What is the purpose of the re-circulator?

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up vote 5 down vote accepted

It helps cool the air faster as it's taking the inside air (already partially cooled) and cooling it further rather than trying to cool the (often hotter) outside air. Obviously there's only a specific range where it works well. I've never noticed a fogging problem using it, but I only use it when it's of benefit...

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Some cars will give you the option to recirculate the air with or without AC, no matter the temperature. On hot days it makes sense to recirculate the cooler air like Brian touched on, and during the winter I sometimes like to recirculate the warmer air on really cold days.

If your windows are fogging up at all when your AC is on, you might have a problem with your AC though.

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