Most of us would find life a little more difficult without our trusty freezer, whether it’s a small freezer combined with our refrigerator or a larger, stand-alone chest freezer. We’d have no way to make ice or keep meat and other foods frozen, so there’d be no way to store some food for a long period of time. A freezer is something we take for granted every day, but most of us don’t know much about how they work to keep food frozen.
A freezer can keep items at a temperature as low as -18 degrees, but how does it do it? The basic explanation is that the freezer takes warm air and cools it. But the technical explanation is a little more complicated. A freezer is made up of a compressor, a condenser, an evaporator, a thermostat and a capillary tube. And frost-free freezers also have small heater coils and a timer that work to keep frost from building up inside the freezer.
A low-pressure gas called a refrigerant is converted into a hot, high-pressure gas in the compressor. This heated gas then travels through the condenser coils, which are bent tubes inside metal that look a lot like the radiator on your car. As it moves through the coils, the heat from the gas dissipates and radiates out from the tubes, and the gas then becomes a liquid.
The capillary tube controls the pressure of this gas as it goes through the coils. Once the gas, now liquid, passes through the end of the capillary tube, it expands and boils. As it moves through the evaporator coils, it evaporates and once again becomes a low-pressure gas. It’s now very cold, and flows through the evaporator coils where it absorbs heat. As it absorbs the heat, it cools down the air going past the coils. The freezer’s fan circulates this cold air throughout the freezer. Then the gas goes back into the compressor and starts the cycle all over again. The thermostat controls when this happens, by sending a signal to the compressor to start when the temperature in the freezer starts to fall. When the temperature drops to the correct number, it turns off the compressor.
Frost-free freezers keep frost from building up in a freezer. The evaporator coils of a freezer are extremely cold so that any humidity in the air of the freezer near these coils instantly freezes. This builds up after a while and forms frost on the walls of the freezer. In a frost-free freezer, a heating element is located just below these coils. The timer causes the heater to kick on at various intervals and the heat causes any frozen moisture on the wall of the freezer to melt away.
Most frost-free freezers work by defrosting briefly 2 to 4 times a day at regular intervals. When the timer kicks the heater on, the cooling system goes off and the compressor won’t run during the time. The melted ice drips into a pan where a fan blows over it to evaporate it.