How Does a Refrigerator Work?
Refrigerators don't really make things cold so much as they take away heat. Inside a refrigerator, it is working to carry the heat energy and pump it outside the appliance. The end result is the same, the temperature inside the freezer drops.
A refrigerator uses a compressor, ammonia or another refrigerant, a long system of tubing, an expansion valve and a couple fans to chill the food stored inside. The refrigeration system is a closed loop and it cycles over and over again to pump out the heat (or to cool off the fridge, if you prefer to think of it that way).
The compressor does as the name implies, it compresses the refrigerant. Compressing a gas causes its temperature to rise, so it is circulated through tubing outside the appliance to allow it to dissipate heat into the room. As the compressed gas cools and reaches the location where it enters the interior of the refrigerator, it passes through an expansion valve and the pressure drops. When the gas goes from a high pressure state to a low pressure state its temperature drops.
A fan circulates the air in the freezer over the now very cold refrigeration tubing. The refrigerant absorbs the heat from the freezer and carries it back outside the appliance to return to the compressor again. A thermostat in the refrigerator monitors the temperature and signals the compressor when to start a refrigeration cycle. Some models have a second thermostat in the freezer for more precise temperature control.
In most refrigerators, the refrigerant passes through the freezer and then the air is circulated between the freezer and the refrigerator to lower the refrigerator's temperature. However, in some models, the refrigerant tubing also passes through the fridge.
A side effect of the drop in air temperature is condensation. The water in the air condenses and forms on the contents and interior of the fridge and freezer. In the freezer it freezes into ice, resulting in frost build-up. Most freezers have an automatic defrost system to control the build-up of ice. The system simply turns cuts the circuit to the compressor and turns on a heater to melt the ice. The cycle runs for a period of time, the ice run-off is channeled to a evaporation tray on the outside of the appliance and when the cycle completes, the circuit to the compressor is restored.
When the refrigerator or freezer door is opened, a door switch turns on the interior light. In some cases the switch also disables some circuits, such as the interior fan or the through-the-door ice and water service.