This is because the air inside your car is saturated with water and can't 'hold' that water anymore. This is what is called 'dew point' (when the water contained in the air starts to condensate).
The condensation then freeze on your window because of the low temperature outside.
Here are a few suggestions:
-Do not leave anything wet inside your car
-Do not recirculate the air
-turning your AC on can actually help to get rid of the extra moisture
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Monday, December 1st, 2008 AT 1:42 PM