A refrigerator cools your food not by creating cold, but by absorbing heat from the inside of the box and pushing it out into your kitchen. It achieves this through a continuous cycle of thermodynamics using a chemical substance called a refrigerant. This refrigerant constantly changes between a liquid and a gas as it travels through a closed loop of tubes and mechanical parts.
The process begins at the compressor, which acts as the heart of the system. The compressor pulls in low-pressure refrigerant gas and squeezes it tightly. This compression forces the molecules together, which dramatically increases both the pressure and the temperature of the gas. The hot, high-pressure gas is then pushed out of the compressor and into the condenser coils, which are the warm metal tubes usually located on the back or underneath the refrigerator.
As the hot gas flows through the condenser coils, it is exposed to the cooler air of your kitchen. The heat from the gas transfers through the metal coils and dissipates into the room. As it loses heat, the high-pressure gas turns into a liquid. This high-pressure liquid then travels toward an expansion valve, which is a tiny, narrow passage.
When the liquid is forced through the small opening of the expansion valve, it enters a low-pressure area. This sudden and severe drop in pressure causes the liquid to expand and cool down incredibly fast, turning it into a freezing cold mist. This cold mixture then flows into the evaporator coils, which are located inside the actual refrigerator compartment.
Because the refrigerant inside the evaporator coils is much colder than the food and air inside the fridge, it naturally draws heat away from the interior space. As the refrigerant absorbs this heat, it boils and evaporates, turning completely back into a gas. The interior of the refrigerator is left cold because its heat was essentially sponged up by the refrigerant. The warmed, low-pressure gas then travels back to the compressor to be squeezed again, starting the entire cycle over. A thermostat monitors the internal temperature of the appliance and simply turns the compressor on or off to maintain the desired level of chill.