I have an 04 A8L and during the day the windows all frost over on the inside. I checked in the vehicle settings menu and made sure that it wasn't in econ mode, which doesn't run the ac compressor to save fuel. My carpets are not wet. No one is breathing hard, and the windows keep fogging/frosting up. Any help would be great.

 

the only time ive seen that is when like you said, water on the inside or maybe a leaky heater core.

 

it could stiill be the heater core, sorta. inside the heater core are a couple of valves that re-direct hot air from the engine-coolant system (which is where the heater gets its' heat from), in small or large increments, depending on how much heat you call for. if the IC that controls that valve (or valves, usually) is confused or malfunctioning, you can get the phenomena you described.

Get it VAG'd, see if you get any codes