I love my 2001 C320. It has been a perfect car but in the last two weeks, I have been having a major problem. As the weather has gotten very cold lately, I cannot get the inside windows to clear off. After ten minutes in the car, all of the windows are entirely fogged up. If I am in the car for more than 30 minutes, ice will form on the inside of the car! The rear defroster works, but as soon as it clears the back window and shuts off automatically, the ice starts building on the inside again. If I turn the front defroster on high, I can clear the windshield halfway up, just enough to see out if I needed to drive the car. I took it to my local mechanic and he cannot find a problem as he said the defroster is working fine. When you let the car sit and run and turn up the heat, all of the windows clear off fine, but whenever I am inside driving, the frost builds up. Maybe bad glass? Maybe I am incompetent? Any help is appreciated.