Capacity Control on the Carrier/Carlyle 06L, 06G, 5H, and 5F40s and 60s is accomplished by mechanically lifting the suction valve disks off the suction seats. When the valve is lifted all refrigerant in the cylinder is pumped back into the suction side of the compressor on the piston up stroke.
The unloader controls are basically the same. The only real difference is where the parts are located on each compressor and slightly differently designed hydraulic relay on the 06L compressors. There are three main components in this system, the needle valve, the hydraulic relay and the power elements.
The needle valve controls the position of the hydraulic relay piston by varying the oil pressure on top of this piston. This oil pressure is referred to as the “control oil pressure” and is the oil that comes thru a small orifice in the top of the relay piston. Pressure is varied by a controlled dumping of this oil back into the crankcase thru a needle valve. Three forces control the needle valve, suction pressure in one direction and the range adjustment spring plus external air pressure or atmospheric pressure in the other direction. A balance to maintain the desired suction pressure is achieved by changing the spring pressure using the external adjusting stem.
The hydraulic relay controls the oil supply from the oil pump to the power elements by opening or closing the supply oil lines to the power elements. Detent balls and springs in the relay control the steps of the relay piston. All the compressors have four steps though on four cylinder machines only three are actually used, the fourth is not piped to any power element.
These compressors can be operated electrically using remotely mounted solenoids piped back to the compressor but when used this way the operation of the oil relay to the power elements must be blocked. The manufacturer offers a kit for converting these compressors to electric unloading.