Abstract: Multiple compressors are connected to a common shaft of a drive motor. Provision may be made for selectively disengaging one or more of the compressors from its drive connection. The multiple compressors an preferably attached to opposite ends of a common motor shaft extending from both ends of the motor. Multiple compressors may be arranged to operate in parallel flow relationship or in series flow relationship in a single refrigerant circuit. The compressors may also be installed on separate refrigerant circuits. In a series flow relationship, a vapor or liquid injection function may be provided. Both compressors may be of an open-drive design, or one of the compressors nay share a common housing with the motor.