Skool me on Aircon...

[mpc]

From what I understand of aircon, when it's on and set to cold it cools and sucks the humidity out of the air (demisting windows quickly etc.)

When it's on and set to hot does it still suck the humidity out of the air?

[kenp]

yes

[Bigglesfliesundone]

This is my understanding (basic as it may be) of air conditioning in the close confines of a car.
The air is cooled the same way your fridge works and is vented into your car. The reason why it demists your car is because cold air can hold a lot less moisture than warm or hot air, therefore it forces the humid air out of the car by replacing it with "drier colder" air (finite volume of the inside of your car and all that)
If you set it to hot the air conditioning no longer works as its a cooler rather than a heater. Setting your temp dial to hot will eventually get rid of the misted wind screen but nowhere as quickly as cold air
Thats my understanding but prepared to be proved wrong

[rich r]

Correct - it cools and dries the air. The aircon unit is before the heater unit, so if you have the heater controls set to hot and aircon on, outside air is drawn in, cooled and dried, then heated. The net result being hot, dry air - which is ideal for demisting windows as the water on the window can readily form a vapour and be carried away from the glass.

The drying happens as said above because cold air can't hold as much moisture as hot air. So as the damp, warm air passes through the aircon evaporator unit, the water vapour becomes liquid. This is then allowed to drip out of a pipe under the car (which is why you often see puddles under cars in hot weather).