Everything the refrigerator removes from the food, plus the energy added by the compressor, leaves through the condenser. In most commercial cabinets it is a copper or aluminium tube coil with thin fins, mounted at the base or top, with a fan pulling room air through it. Some chest freezers and small units use a skin condenser instead, with tubing bonded to the inside of the outer cabinet walls.
A condenser only works if air can flow through it and that air is not too hot. Flour dust in a bakery, oily vapour near a tandoor and lint in a shop all build up on the fins and act like a blanket. Pushing a unit tight against a wall or into an alcove next to an oven has the same effect: the compressor runs at higher pressure, draws more power and may trip.
Cleaning the condenser with a soft brush or vacuum every month or two in a dusty or greasy kitchen is the most useful maintenance task an operator can do. In coastal cities, corrosion-protected fins are worth asking about, because salty, humid air slowly eats bare aluminium.