The demisting effect of air conditioning is easy to explain - when the air blows over the evaporator it is chilled and condenses out much of the moisture present. When you blow this very dry air over the windows, it picks up the moisture, even though it is cold. Depending on how your car controls work, if you have a simple car (a/c button and simple heat control, versus "climate control") then the best demisting of all is to turn on the a/c and turn the heater temperature control up.
Which, to bring this back to aviation, is actually how moisture is removed from the cabin of some light jets. For example, the CE525's don't have an air cycle machine, they have separate warm bleed air and refrigerant based air conditioning. In normal operation, the air conditioner only cycles on when the cabin is too warm - the "climate control" model. But, when you switch on the defog system in the descent, it forces the a/c compressor and forward evaporator to run, thus removing moisture from the air that it then blows on the inside of the windshield. Because this air is cold, the cockpit also gets extra (warm) bleed air flow from the flow divider.
Sadly, the two don't quite meet, and the result is that 525 crew suffer hypothermia on every descent...
