Patent ID: 8366406

Claim:
A multi-stage compressor comprising: a lower stage compression mechanism and a higher stage compression mechanism that are provided in a closed housing and driven by an electric motor, wherein an intermediate pressure refrigerant gas which has been compressed by the lower: stage compression mechanism is discharged into the closed housing, and the intermediate pressure refrigerant gas is sucked into the higher stage compression mechanism, thus performing two-stage compression, and an injection circuit for injecting an intermediate pressure refrigerant extracted from a refrigerant circuit into the closed housing is provided, the multi-stage compressor characterized in that: the injection circuit is branched into a plurality of circuits, a first circuit thereof being communicatively connected to an inside space of the closed housing that is at a same side as the higher stage compression mechanism with respect to the electric motor, and a second circuit being communicatively connected to an inside space of the closed housing that is opposite from the higher stage compression mechanism with respect to the electric motor; and the first circuit and the second circuit are provided with a switching mechanism for switching the injection circuit to either the first circuit or the second circuit according to a dryness of the injection refrigerant.