Capability control apparatus for a compressor

A capability control apparatus for a compressor including a compressor chamber, comprising means for forming a suction effect region separate from said compressor chamber, a bypass hole for providing communication between said compressor chamber and said suction effect region, said bypass hole having a first end opening to said compressor chamber and a second end opening to said suction effect region, and an unloader piston arranged in said suction effect region and being movably displaceable relative to the second end of said bypass hole for opening and closing said bypass hole, said unloader piston having first surfaces and separate oppositely directed second surfaces thereon and in said suction effect region the first surfaces being acted upon by the in-cylinder pressure of said compressor chamber and a suction opening arranged in said suction effect region so that the absolute pressure acting through said suction opening acts on said second surfaces, and said unloader piston arranged to open the second end of said bypass hole when the absolute pressure acting through the suction opening acts on said second surfaces rises above a predetermined value and to close the second end of said by-pass hole when the absolute pressure acting through the suction opening drops below the predetermined value.