Steam machines from the garment industry have become quite useful in the window tinting market. Normally used to remove wrinkles from clothes, these portable steamers help remove old film quickly and easily and will save you valuable time.
Using a steamer is effective in removing pressure sensitive adhesives, allowing 90% of the adhesive to come off the glass with the film. Any residual adhesive left behind on the window can simply be removed by waiving the steamer over the area, and then wiping off with a paper towel.
Additionally, using the steamer on tougher dry adhesive films can help to loosen the adhesive as well. However, there will be times (maybe 10%) when the adhesive just won't come off. At that point, it's best to fall back on the tried and true method of scraping the adhesive off the glass.
Note: Using a steam machine on a dual pane window is not recommended. It may cause thermal stress fracture or create seal failure.