I noticed, by accident, that the defrost setting keeps the car comfortably cool in the summer. I mentioned this to my teenage son, who then asked, "well, what does the defroster run off of?" I told him I really didn't know, but maybe it was the compressor for the A/C. So anyway, I tried it again on a rather warm day, and later noticed my windshield had a foot-long crack. I had the temperature set at the coolest setting, but did not have the A/C button pushed in. Was the crack in the windshield just a coincidence? Or did I do it by running a cool defrost on the windshield?