Almost every commercial refrigerator and freezer works on the vapour-compression cycle. Liquid refrigerant at low pressure enters the evaporator inside the cabinet, boils at a temperature well below that of the food, and soaks up heat as it turns to vapour. The compressor then draws that vapour away and squeezes it to a high pressure, which also raises its temperature.
The hot vapour travels to the condenser, usually the finned coil at the back or base of the unit. A fan pushes room air across it, the refrigerant gives up its heat and condenses back into a liquid. That liquid passes through a restriction, a capillary tube or an expansion valve, where its pressure drops sharply so it is ready to boil again in the evaporator. The loop repeats for as long as the controller calls for cooling.
The key idea is that a refrigerator does not create cold; it moves heat. Heat taken out of the paneer, milk and marinated chicken in a restaurant reach-in, plus the heat of the compressor's own work, has to be dumped into the kitchen. In a 40 °C kitchen the condenser has to work harder to reject that heat, which is why capacity and running cost depend so much on where the unit stands.