A reciprocating compressor (10S;10M) for refrigerant, the compressor comprising: a first cylinder and a second cylinder; movable reciprocal pistons disposed in the cylinders; a first suction cutoff unloader valve assembly integral to the compressor and adapted for pulse width modulation cycling to interrupt flow of the refrigerant to the first cylinder; a second suction cutoff unloader valve assembly integral to the compressor and adapted for pulse width modulation cycling to interrupt flow of the refrigerant to the second cylinder; and a controller configured to operate at least one of the suction cutoff unloader valve assemblies in pulse width modulation cycling and monitor a number of pulse width modulation cycles for at least one of the suction cutoff unloader valve assemblies; wherein operating in pulse width modulation cycling achieves a variable part-load capacity; characterised in that the controller is configured such that pulse width modulation cycling includes an alternating cycling mode that operates the first suction cutoff unloader valve assembly in pulse width modulation cycling, while the second suction cutoff unloader valve assembly is not operated in pulse width modulation cycling but is disposed either in a fully unloaded position blocking the flow of refrigerant to the second cylinder or a fully loaded position allowing for uninterrupted flow of refrigerant to the second cylinder, and the controller is configured to operate the first suction cutoff unloader valve assembly in pulse width modulation cycling for a first time period and the controller does not operate the second suction cutoff unloader valve assembly in rapid cycling during the first time period and then the controller operates the second suction cutoff unloader valve assembly in pulse width modulation cycling for a second time period and does not operate the first suction cutoff unloader valve assembly in pulse width modulation cycling during the second time period; and wherein the controller counts the number of cycles for each suction cutoff unloader valve assembly and alternates the first and second suction cutoff unloader valve assemblies based on the counted number of cycles to assure that the first suction cutoff unloader valve does not cycle a number of times more than the second suction cutoff unloader valve. a first cylinder and a second cylinder; movable reciprocal pistons disposed in the cylinders; a first suction cutoff unloader valve assembly integral to the compressor and adapted for pulse width modulation cycling to interrupt flow of the refrigerant to the first cylinder; a second suction cutoff unloader valve assembly integral to the compressor and adapted for pulse width modulation cycling to interrupt flow of the refrigerant to the second cylinder; and a controller configured to operate at least one of the suction cutoff unloader valve assemblies in pulse width modulation cycling and monitor a number of pulse width modulation cycles for at least one of the suction cutoff unloader valve assemblies; wherein operating in pulse width modulation cycling achieves a variable part-load capacity; characterised in that the controller is configured such that pulse width modulation cycling includes an alternating cycling mode that operates the first suction cutoff unloader valve assembly in pulse width modulation cycling, while the second suction cutoff unloader valve assembly is not operated in pulse width modulation cycling but is disposed either in a fully unloaded position blocking the flow of refrigerant to the second cylinder or a fully loaded position allowing for uninterrupted flow of refrigerant to the second cylinder, and the controller is configured to operate the first suction cutoff unloader valve assembly in pulse width modulation cycling for a first time period and the controller does not operate the second suction cutoff unloader valve assembly in rapid cycling during the first time period and then the controller operates the second suction cutoff unloader valve assembly in pulse width modulation cycling for a second time period and does not operate the first suction cutoff unloader valve assembly in pulse width modulation cycling during the second time period; and wherein the controller counts the number of cycles for each suction cutoff unloader valve assembly and alternates the first and second suction cutoff unloader valve assemblies based on the counted number of cycles to assure that the first suction cutoff unloader valve does not cycle a number of times more than the second suction cutoff unloader valve.