Try the Air Conditioner

Whenever this happens it's usually when the relative humidity is high, but the ambient temperature of the outside air has suddenly cooled down. This causes the humid air in your car to condense onto the windshield. Blowing hot air will always help, because when the windshield heats up, the water vapor can no longer condense onto it; but this takes some time and can initially make it worse as you noticed. I always found that turning the air conditioner on for a few minutes (even in up north here in the winter!) will almost immediately remove the moisture. An air conditioner is essentially a de-humidifier as I'm sure you've noticed from the comfort level they provide in hot humid climates. I wonder if recycling the air has any effect, seeing as the moisture is condensed out on the air conditioner's coil anyway? You'll have to experiment.

In the winter, our cars get terribly wet inside from the snow that gets tracked in and melted on a constant basis no matter how careful we are. Eventually it evaporates inside the car often causing the problem you described. (In extreme cases I've even had to scrape the frost off the inside of my windshield with an old credit card.)

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