Which type of compressor is known not to include a capacity control?

The rotary compressor is known for its simplicity and compact design, which typically does not incorporate a capacity control mechanism. Rotary compressors operate using a rotating element that compresses the refrigerant directly, allowing for a steady flow and efficient operation at a constant capacity. This attribute makes them ideal for applications where variable capacity isn't necessary, such as in small air conditioning systems or refrigeration units.

In contrast, other types of compressors, like reciprocating, screw, and scroll compressors, can often be equipped with capacity control features. These controls allow for adjustments in the compressor's output to better match the cooling demand, improving efficiency and performance, especially in larger or more sophisticated systems. Thus, the absence of a capacity control in rotary compressors is a defining characteristic that aligns with their operational design and common usage.