Refrigerators

So for untold months, my frost-free refrigerator has not been exactly what you would call frost-free. That means that it kept building up lots and lots of ice on the inside that would need to be scraped off from time to time. Last night, I hear some funny sounds, but don't really think much of them. The next time I open the refrigerator, almost all the ice is suddenly gone. The funny sounds were bits of ice falling off as they melted. So I guess that means that the frost-free part is now suddenly working. What was so special about yesterday that it caused it to start working after not working for so long?