I don't rely on the defroster to clear ice off my windshield, I use a scraper for that. But what I have noticed is difficulty keeping the windshield clear on really damp days, regardless of outside temp. I can barely keep a small viewing area open on the windshield and the front drivers and passenger windows, but forget the rear door or rear window glass. I don't think the defroster vents are aimed properly, or they don't have the proper dispersal pattern for the greenhouse on these vehicles.