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Old 07-29-2013, 05:09 AM
RhoXS RhoXS is offline
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Location: Florida
Join Date: May 2008
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Mein Auto: Z3 & X3
Originally Posted by The X Men View Post
Why don't you just turn on the AC on humid days?
Using the A/C is exactly why the rear window fogs up.

The A/C lowers the temperature of the glass below the dew point for the conditions outside the car. The fogging occurs on the outside of the glass, not the inside. The rear defogger raises the temperature of the glass slightly, to just above the dew point so no moisture condenses out on its surface. This is the same phenomena that causes water to condense out on the outside surface of a glass of ice water.
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