Patent ID: 8863533

Claim:
A method for operating a refrigerating cycle apparatus having a low-stage compressor and a high-stage compressor connected to each other in series, and a refrigerant switching valve connected to a discharge side of the high-stage compressor and having a low-stage side outlet connected to a low-stage side evaporator and a high-stage side outlet connected to a high-stage side evaporator, with the low-stage side evaporator connected to a suction side of the low-stage compressor and the high-stage side evaporator connected to a suction side of the high-stage compressor, the method comprising: determining that oil balancing is required between the low-stage compressor and the high-stage compressor; and performing an oil balancing operation and transferring oil from one of the low-stage or the high-stage compressor to the other of the low-stage or the high-stage compressor, the one of the low-stage or the high-stage compressor containing more oil than the other of the low-stage or the high-stage compressor, wherein performing of an oil balancing operation comprises: opening both the low-stage side outlet and the high-stage side outlet of the refrigerant switching valve for a preset time with the low-stage compressor and the high-stage compressor turned off, so as to discharge oil from the one of the compressors containing more oil to the other of the compressors containing less oil; introducing oil discharged to the refrigerating cycle into the other of the compressors containing less oil; and after discharging the oil to the refrigerating cycle, driving both the low-stage compressor and the high-stage compressor for a preset time, with the low-stage side outlet of the refrigerant switching valve open and the high-stage side outlet thereof closed, and introducing the oil within the refrigerating cycle into the low-stage compressor.