How does a refrigerator actually keep things cold?

A refrigerator keeps things cold by moving heat out of the interior rather than "pumping in cold." It does this using a process called the vapor-compression cycle. Here is how it works in four simple steps:

1. Evaporation (Taking heat in): Inside the walls of your fridge, there is a tube filled with a cold, liquid refrigerant. As this liquid moves through the evaporator coils, it absorbs heat from the food inside the fridge. This causes the refrigerant to boil and turn into a low-pressure gas.
2. Compression (Adding pressure): That gas travels to a compressor (the motor-driven pump on the outside of the fridge). The compressor squeezes the gas, which raises its pressure and significantly increases its temperature.
3. Condensation (Releasing heat): The hot, high-pressure gas flows into the condenser coils—those black, grid-like tubes usually found on the back or bottom of the fridge. Because the gas is much hotter than the room air, it releases its heat into your kitchen. As it loses heat, the gas turns back into a liquid.
4. Expansion (Cooling down): The liquid refrigerant passes through an expansion valve, which acts like a tiny nozzle. This suddenly drops the pressure, causing the refrigerant to rapidly expand and turn back into a very cold liquid, ready to return to the fridge interior and start the cycle all over again.

Essentially, your refrigerator acts like a heat pump, gathering warmth from your leftovers and discarding it into your kitchen. That is why the back or bottom of a fridge often feels warm to the touch.