Re: How does the rear defogger in a car work

Unfortunately, the answer is not quite as exciting as you may have hoped. Your average rear window defroster is just a simple electric heating grid. The lines are made of a mixture of metal and some sort of adhesive or resin to bond it to the window. It works just like any other electric heater. An electric current is passed through the grid, and the electrical resistance creates heat. It normally doesn't feel warm, because it doesn't have to get very warm to do it's job. To melt ice or snow, it only needs to warm the window to a temperature just above freezing (32 degrees F). That will still feel pretty cold to the touch, but it's warm enough to do its job. Most defrosters are made to switch off long before they start to get warm. If they got too warm, it would require extra (and unnecessary) power from the car, and it would also have the potential of cracking the glass from such a rapid change in temperature. I hope that answers your question. Thanks for writing!

Your Mad Scientist
Mike Scannell