What type of control is normally used for unloading a compressor?

A pressure switch is the most commonly used control for unloading a compressor because it monitors the pressure within the system and activates or deactivates the compressor based on predetermined pressure levels. When the pressure exceeds a set limit, the pressure switch can signal the compressor to unload, which reduces the load on the compressor during periods of low demand or when it is not required to operate at full capacity. This is particularly important for systems that require variable capacity operation, allowing for more efficient energy use and preventing wear on the compressor due to continuous cycling.

Other control types have specific applications but differ in purpose. A camshaft controlled valve is primarily found in engines and may not be applicable to the unloading of refrigerant compressors. A thermostatic switch is typically used for temperature control, not pressure control, while an eccentric controlled valve operates based on mechanical motion rather than reactive pressure levels. Thus, the use of a pressure switch is most suited for the role of unloading compressors in refrigeration systems.