PROBLEM TO BE SOLVED: To provide a refrigerant pipe washing method capable of stably recovering residual oil in a refrigerant pipe system by a washing operation even if a large quantity of liquid refrigerant resides in a high-pressure gas pipe at a time of updating a cooling/heating multi-split air conditioner while reusing the existing refrigerant pipe system.;SOLUTION: At a time of washing three pipes of a high-pressure gas pipe 4, a low-pressure gas pipe 5, and a high-pressure liquid pipe 6 led out from an outdoor unit 2, a cooling/heating multi-split air-conditioner 1 is caused to operate in a state of connecting an oil recovery device 19 to the low-pressure gas pipe 5 to first flow superheated gas discharged from a compressor to the high-pressure gas pipe 4 so as to recover residual oil in the high-pressure gas pipe 4 together with liquid refrigerant or the like, while performing a preparatory operation for evaporating refrigerant by actuating heating means 23 of the oil recovery device 19, and the air-conditioner 1 is then set into a liquid pack operation state with an electronic expansion valve 18 of each indoor unit 3 slightly opened, thereby performing a washing operation for washing the three pipes of the high-pressure gas pipe 4, the low-pressure gas pipe 5, and the high-pressure liquid pipe 6.;COPYRIGHT: (C)2015,JPO&INPIT
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