Moisture in car causing frost to windows

There must be an unusually high level of moisture in your car if even the Defrost (A/C) won't clear it. My Ford sedan was doing that and I found a gallon of water sloshing around in the trunk where my spare tire was half submerged. I dried it out and found water was getting in at the trunk lid gasket. Look around for water accumulating somewhere.

Mouse turds is your clue. I had a 2001 Audi A4, one day the windows wouldn't defog, the ac system worked perfectly (it appears you already know that the defrost setting turns on the ac compressor to dry the defrost air), I had to run the rear defrost to see out of the back as well. Turned out, the area under under the cabin air filter rusted away, and when it rained water would get under the passengers side carpet. Turning on the heat would essentially turn the car into a steam room. It appears something similar has happened. I'm guessing the mouse chewed it's way in somewhere, probably through one of the rubber plugs in the firewall, and now water is getting in under the carpet or on the sound deading padding when it rains or is being driven when the roads are wet....

Yeah, sounds like you got a critter in there and it built a nest somewhere in the duct or heater core. Your defroster should clear that window once the engine is warmed up, if not then a vent is blocked. Even if the critter is gone the nest may still be there.

No water found in vehicle that I can see or feel. If there was a nest you would think the air blowing would be less correct? Anyone know the best way to look in heats and or air ducts???camera?? Vs taking down front dash??

Automotive carpet has a rubber backing behind the fibers, if the water is under the carpet you won't see it until it starts fogging stuff up. The hvac intake area could have its drains plugged as well, with a mouse nest or something. This would be under the black plastic wiper tray under the windshield, but its unlikely. A quick deduction of the problem reveals that this happens when the heat is on, car heaters on heat the interior of the vehicle. Somewhere in there is an area that is getting wet and capable of quickly wicking away the moisture when warm air is blown across it. I'm going with the problem is water getting inside the car. And yes, a nest directly inside of the interior vents would restrict airflow at at least one of the outlets.