A method for replacement of a part of a refrigeration cycle apparatus including a compressor that compresses a flammable refrigerant, a first heat exchanger capable of functioning as a condenser condensing the refrigerant by heat exchange, an expansion device that controls a pressure of the refrigerant, a second heat exchanger capable of functioning as an evaporator evaporating the refrigerant by heat exchange, a first refrigerant flow closing device , and a second refrigerant flow closing device , the compressor , the first heat exchanger, the expansion device , and the second heat exchanger being connected by pipes to form a refrigerant circuit (A), the first and second refrigerant flow closing devices controlling a flow of the refrigerant into and out of an outdoor unit by opening and closing, the outdoor unit accommodating at least the compressor and the first heat exchanger, the method comprising: an operation step of performing an operation in which the first heat exchanger functions as a condenser and the second heat exchanger functions as an evaporator; a pump-down step, being performed subsequently, of closing the first refrigerant flow closing device to stop the flow of the refrigerant out of the outdoor unit, allowing the refrigerant in a pressure reduction section excluding the outdoor unit in the refrigerant circuit (A) to flow into the outdoor unit so as to be recovered therein, and reducing a pressure in the pressure reduction section until the pressure becomes equal to or less than a set pressure or a time equal to or greater than a setting time elapses; a flow closing step, being performed subsequently, of closing the second refrigerant flow closing device and stopping the compressor ; and a part replacement step, being performed subsequently, of removing the part from the refrigerant circuit (A) by heating to replace the part, the part replacement step being performed after the pressure in the pressure reduction section has become equal to or is less than the set pressure, wherein the set pressure is a pressure less than a value expressed by LFL × 1000 × R × T/M (Pa) where M (g/mol) denotes a molecular weight of the refrigerant, R (Pa × L/K × mol) denotes a gas constant, T (K) denotes a typical temperature of the refrigerant in the refrigerant circuit (A), and LFL (kg/m 3 ) denotes a lower flammability limit of the refrigerant. an operation step of performing an operation in which the first heat exchanger functions as a condenser and the second heat exchanger functions as an evaporator; a pump-down step, being performed subsequently, of closing the first refrigerant flow closing device to stop the flow of the refrigerant out of the outdoor unit, allowing the refrigerant in a pressure reduction section excluding the outdoor unit in the refrigerant circuit (A) to flow into the outdoor unit so as to be recovered therein, and reducing a pressure in the pressure reduction section until the pressure becomes equal to or less than a set pressure or a time equal to or greater than a setting time elapses; a flow closing step, being performed subsequently, of closing the second refrigerant flow closing device and stopping the compressor ; and a part replacement step, being performed subsequently, of removing the part from the refrigerant circuit (A) by heating to replace the part, the part replacement step being performed after the pressure in the pressure reduction section has become equal to or is less than the set pressure, wherein the set pressure is a pressure less than a value expressed by LFL × 1000 × R × T/M (Pa) where M (g/mol) denotes a molecular weight of the refrigerant, R (Pa × L/K × mol) denotes a gas constant, T (K) denotes a typical temperature of the refrigerant in the refrigerant circuit (A), and LFL (kg/m 3 ) denotes a lower flammability limit of the refrigerant. <EOS>