Inside a reciprocating compressor, a crankshaft turned by the electric motor drives one or more pistons. On the down-stroke, suction gas is drawn in through a thin reed valve; on the up-stroke it is compressed and pushed out through the discharge valve. The design has been refined over decades for refrigerators and freezers and is well understood by technicians everywhere.
It suits the small capacities found in reach-ins, undercounters, chest freezers and visi coolers. It copes with a wide range of evaporating temperatures, so variants of the same basic design serve both chillers and deep freezers, and replacement compressors in standard sizes are easy to source from refrigeration traders in most Indian cities.
The trade-offs are more moving parts, a little more vibration and noise than rotary or scroll types, and sensitivity to liquid refrigerant reaching the cylinder, which can break valves. A reciprocating compressor that knocks, hums without starting or trips on overload is usually pointing to low voltage, a failed starting component or liquid floodback.