Removing old film on the back window of a 1996 Toyota Camry without damaging defroster lines.

Method 1: Repeated scraping will eventually damage or remove the defroster lines, and scraping around them is nearly impossible. The best way to remove an old film is to use the trash bag method: Soak the whole window in heavy ammonia and then cover it with a black trash bag. Then place the car in a hot place or the sun for an hour, and try lightly scrubbing or scaping off the film.  Method 2: Sometimes these old films can be really stubborn, so if you aren’t able to remove the film using the previous method, it could be easier just to explain the situation to the customer and then replace the whole window.