Capacity Control on the Carrier/Carlyle 06D and 06E compressors is accomplished in one of two ways, hot gas by-pass (HGBP) or suction cut-off unloading (SCOU).
Both types can be electrically controlled with a solenoid or operated with a pressure operated capacity control valve. The suction cut off shown here consists of the unloader head assembly and the unloader control. The unloader head has three chambers, one connected to the suction side of the compressor, a second connected to the cylinders of that bank and the third connected to the discharge side of the compressor. The suction chamber and the cylinder chambers are connected by means of a controlled passage. This passage can be open or closed depending on the position of the unloader piston. When open, the cylinders of the unloader bank and the suction side of the compressor are connected and the compressor is loaded. When closed, the cylinders of that bank are denied gas from the suction side of the compressor, hence the name “suction cut-off”.
These compressors are shipped with a blocking sleeve in all unloader heads. This sleeve manually opens the unloader valve and loads the compressor. If a capacity control valve is installed this sleeve must be removed.
Proper operation of the unloader control valve should be checked when installed. This includes the control set point and differential settings on the pressure operated control valve. An improperly installed or defective control valve can result in compressor failure.