When the temperature stays a few degrees below freezing all day, the ice and snow melted by a car's defrosters will refreeze and need to be scraped off next time. I wondered if I could alleviate this problem and I tried it on a day when it did stay so cold—and when it was snowing.
About 5 minutes from my destination, I turned off the car's interior heat altogether. It didn't affect the interior temperature too much, but I figured the windshield surface would quickly cool to freezing as well. (The cooling of the windshield was enhanced by car's forward motion equating to a stiff wind blowing on it.) I minimized use of the windshield washer, only enough to keep the windshield clear.
The next day, the car was covered in snow. But the surface of the windshield—and all the glass for that matter—was free of ice. The snow had not melted-then-froze (on what would have been the warmed glass) so there was nothing to scrape, and it swept off cleanly. Trying it several more times, it appears to work when the air temperature is far below freezing (lower than -5°C / 20°F) otherwise the glass just doesn't cool enough.
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