Whatever you do, if your car allows it, do NOT run the defroster with the air circulation switch to "recirculate." A lot of cars will not provision for this arrangement, but I've seen some, especially Japanese ones, which let you turn on the Defroster and Select Recirculate. When you don't let the air escape, and/or bring in fresh air, the windows will fog up (condensation) even with the Def on. This is true even when it's raining out. A Toyota Dealer told me that the Camry I was driving did that because of the difference in moisture levels inside and outside the car. He said it was a major complaint with the cars, even though there was nothing wrong with it. Even in the Owners Manual, it tells you the proper use. The car was a late 90's model, and I'm not sure if they made the correction to not allow you to do this anymore. I know when I switch my Buick's Automatic HVAC unit to Defroster, it locks out the Recirc button.
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