Air-conditioning system

An air-conditioning system wherein a single heat source unit having a compressor, a four-way valve, a heat source unit side heat exchanger and an accumulator is connected to a plurality of indoor units having an indoor side heat exchanger and a first flow rate controller through first and second connection pipes;

• a first branch joint including a valve device for selectively connecting one of said plurality of indoor units to said first connection pipe or said second connection pipe and a second branch joint connected to another of said indoor side heat exchangers of said plurality of indoor units through said first flow rate controller and connected to said second connection pipe through a second flow rate controller are connected to each other through said second flow rate controller and a gas-liquid separating unit;
• said second branch joint and said first connection pipe are connected through a fourth flow rate controller;
• said second branch joint and said first connection pipe are connected through a bypass pipe having a third flow rate controller therein;
• and
• said air conditioning system comprises;
• a first heat exchanger portion for carrying out the heat-exchanging between said bypass pipe between said third flow rate controller and said first connection pipe and pipings connecting said second connection pipe and said second flow rate controller;
• a flow path change over unit for allowing, when said heat source unit side heat exchanger is operated as a condenser, a flow of a refrigerant from a refrigerant outlet side of said condenser only to said second connection pipe and a flow of the refrigerant from said first connection pipe only to said fourth-way valve side, and allowing, when said heat source unit side heat exchanger is operated as an evaporator, a flow of the refrigerant from said first connection pipe only to a refrigerant inlet side of said evaporator and a flow of the refrigerant from said four-way valve only to said second connection pipe;
• and
• a junction unit disposed between said heat source unit and said plurality of indoor units, said intermediate unit comprising said first branch joint, said second branch joint, said gas-liquid separator, said second flow rate controller, said third flow rate controller, said fourth flow rate controller, said first heat exchanging portion and said bypass pipes;
• characterized by the provision of:
• a first bypass circuit which is connected between said first connection pipe and said second connection pipe and which is opened during the defrosting operation, wherein said second connection pipe is maintained at a high pressure and said first connection pipe is maintained at a relative low pressure with respect to said second connection pipe and upon opening of said first bypass circuit for a defrosting operation refrigerant from the high pressure second connection pipe flows through said first bypass circuit and flows directly into the low pressure first connection pipe.