Multi-air conditioner for heating and cooling including a shut-off valve between indoor and outdoor units and control method thereof

A method for controlling a multi-air conditioner for heating and cooling, the multi-air conditioner comprising at least one indoor unit installed in an indoor space and comprising an indoor heat exchanger and an indoor expansion valve, an outdoor unit connected to the indoor unit via a refrigerant pipeline and comprising at least one outdoor heat exchanger, at least one compressor, at least one outdoor expansion valve, and at least one four-way valve, and at least one leak shut-off valve provided on the refrigerant pipeline, a subcooling unit having a subcooling heat exchanger that cools the refrigerant from the outdoor heat exchanger and runs the refrigerant to the refrigerant pipeline, an accumulator that stores the refrigerant and provides the refrigerant to the compressor;

• an accumulator bypass pipeline that connects the accumulator and the subcooling heat exchanger, and a subcooling bypass valve disposed on the accumulator bypass pipeline, the method comprising:
• detecting a refrigerant leak from the refrigerant pipeline in the indoor space;
• upon detecting the refrigerant leak, blocking a flow of refrigerant by closing the at least one leak shut-off valve installed on the refrigerant pipeline;
• and
• opening the subcooling bypass valve to connect the refrigerant pipeline to an output terminal of the accumulator for decreasing a pressure of the refrigerant in the refrigerant pipeline while the at least one leak shut-off valve is closed.