In the common rolling-piston rotary compressor, an eccentric roller turns inside a round cylinder. A spring-loaded vane keeps the suction and discharge sides apart, and as the roller turns it traps vapour and squeezes it towards the discharge port. There is no up-and-down motion, so it runs with less vibration than a piston compressor of similar size.
Rotary compressors are used widely in room air conditioners and appear in some refrigerators, bottle coolers and compact commercial units, often paired with inverter drives. They are small for their capacity, which helps designers save space in undercounter and countertop units where every centimetre of storage counts.
Because the internal clearances are very tight, a rotary compressor depends on clean, dry refrigerant and the correct oil. Contamination after a poor repair, such as moisture left in when a technician skips proper evacuation, shortens its life. In a busy café where the unit sits near customers, the lower noise is a genuine benefit.