The compressor is the heart of the refrigeration system and the component that uses most of the electricity. In commercial cabinets it is almost always a hermetic type: the motor and pump are sealed inside one welded steel shell, cooled by the returning suction gas, and cannot be opened for repair. If the motor or valves fail, the whole compressor is replaced.
Small reach-ins, undercounters and visi coolers typically use reciprocating or rotary compressors; larger multi-door units and some freezers may use scroll compressors. Many newer designs use a variable-speed inverter compressor instead of a fixed-speed one. The compressor is matched to the refrigerant, the evaporating temperature (a freezer compressor is not the same as a chiller compressor) and the expected ambient.
A compressor runs hot by design, but it should not run non-stop or trip repeatedly. In an Indian shop the usual killers are a choked condenser that raises discharge pressure, low-voltage starts during evening peaks, and frequent power cuts that make it try to restart against high pressure. A healthy compressor starts cleanly, runs without knocking and cycles on and off.