How does a fridge actually make things cold?

It does not make cold — it moves heat, pumping it from inside the cabinet to the room, which is why the back of a fridge is warm and why leaving the door open heats a kitchen rather than cooling it.

The cycle, in four stages:

Compression. A compressor squeezes refrigerant gas, raising its pressure and, as a consequence, its temperature — now hotter than the room.

Condensation. The hot gas flows through coils on the outside, where it loses heat to the room and condenses into a liquid. This is where the heat actually leaves.

Expansion. The high-pressure liquid passes through a narrow expansion valve into a low-pressure region. The sudden pressure drop makes it expand and cool dramatically — the same effect that makes an aerosol can go cold in your hand.

Evaporation. The cold liquid runs through coils inside the cabinet, where it absorbs heat from the food and evaporates. Evaporation absorbs a great deal of energy, which is what does the work. The gas returns to the compressor and the cycle repeats.

The key physical insight is that a substance absorbs large amounts of heat when it changes from liquid to gas and releases it when it changes back. The refrigerant is chosen so those changes happen at convenient temperatures and pressures, and it is never consumed — a sealed system runs for decades on the same charge.

Why this does not violate thermodynamics. Heat does not move from cold to hot on its own; the compressor supplies the work that makes it happen, and the electricity used ends up as heat in the room too. The room always gains more heat than the fridge loses.

A heat pump is the same machine, run for the other side, which is why heat pumps can deliver several units of heat per unit of electricity: they are moving heat, not creating it.

Refrigerants matter environmentally. CFCs damaged the ozone layer and were phased out; several replacements are powerful greenhouse gases and are themselves being phased down.