1. Ingenious inventions

In a non-frost-free freezer, water vapor from the air condenses and then freezes on the cooling coils in the freezer (or on the plastic of the freezer compartment covering the coils). If you put off defrosting long enough, eventually so much ice accumulates that there is no longer room for even a TV dinner.

Frost-free freezers prevent this buildup by doing a mini-defrost every six hours or so. A timer turns on a heating coil, which surrounds the cooling coils, and a temperature sensor turns off the heater when the temperature starts rising above freezing.

The air or ...

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