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Hi
If anyone knows that on a refrigeration system employing cylinder n loading as a method of capacity control , when will comp cylinder begin to load?
When suction pressure starts to increase or decrease

http://www.hawsepipe.net/chiefhelp/AC&R/Refrigeration.htm

QuoteSuction pressure increases or decreases according to increases or decreases in the refrigeration load requirements of the plant. After the temperature pull-down period with a subsequent decrease in suction pressure, the capacity control valve moves to increase the control oil bleed to the crankcase from the hydraulic relay. There is a resulting decrease in control oil pressure within the hydraulic relay. This decrease allows the piston to be moved by spring action. This action successively closes oil ports and prevents compressor oil pump pressure from reaching the unloader power elements. As oil pressure leaves a power element, the suction valve rises and that cylinder unloads. With an increase in suction pressure, this process is reversed, and the controlled cylinders will load in succession. The loading process is detailed in steps 1 through 7 in the figure above.

Suction pressure increases to load, and decreases to unload.

Thanks