Originally Posted by hcbflash
nope. moisture is removed by lowering the temperature of the air and water precipitates. The A/C compressor is used like a "heat pump" and thereby produces warm(er) air and cold(er) air instantly. The warm air is used for defrost purposes and the engine temperature is not lowered by using it's heat for defrosting while it is still not up to an optimum operating temperature.
Warmer air can contain more water (as vapor) than cooler air. This improves the evaporation of the frost and fog on the inside of the vehicle.
Half right, half wrong.
The red parts above are totally incorrect.
The rest is correct.
The "hot" part ( the heat from compression ) is only dumped to the exterior atmosphere of the car, up front, by the radiator. Only chilled air makes it into the vehicle's cabin from the evaporator. Yes, it is the chilling part that removes moisture, and hence "fogging" of the window. The chilled air, already dried, is then heated by the engine's waste heat, and you have warm, dry air.
The A/C is never used in below freezing conditions. Hence, it is not used for defrosting
but only for defogging
. The A/C will not activate the compressor below 33 degrees F, even though the light on your dash may come on, because the light is just in a switch and is not "aware" of the temperature.
Hope that helps all intersted parties.