How to ice proof your car windows. Expecting frost overnight? Just fill a spray bottle with three parts vinegar to one part water and spray on your car windows at night. In the morning, they should be clear of the icy mess. How does it work? Vinegar contains acetic acid, which raises the melting point of water – preventing water from freezing. What to do if you wake up to an already frozen car? Just spray the mixture on your window and watch it melt.