Abstract: The disclosed system includes first and second hermetic shell compressors, one of which always runs while the system is operating and includes unloading means for running at half load, and the other compressor operating at full load or not at all so that four operating capacity steps are available, both of the compressors having shells with suction gas inlets, oil equalizer line ports, and gas exchange line ports being identically sized and located with respect to each other so that standard compressors can be stocked and used in the multiple compressor system while the multiple compressor system is capable of being operated at the varying capacities.

Abstract: A variable capacity multiple compressor refrigeration system having first and second compressors with the first compressor to be always running when the system is operating and the second compressor to be cycled off or to vary the capacity of the system on while the first compressor continues to run. The discharge lines of both compressors are connected together in parallel to the system and a check valve is provided in the discharge line connection between the compressors to prevent discharge pressure from the operating compressor from entering the discharge port of the nonrunning compressor. A by-pass line connects the suction of the system at the inlet of the second compressor to its discharge line between the check valve and its discharge port and a solenoid valve in the by-pass line is arranged to be closed when the second compressor is running and open when it is cycled off.