Conventionally, there have been utilized air conditioning systems where plural outdoor units and plural indoor units are interconnected such that plural refrigerant systems are formed.  In such air conditioning systems, an outdoor unit and the indoor units connected to that outdoor unit are regarded as belonging to the same refrigerant system, and air conditioning control is performed per refrigerant system. 
Additionally, in the air conditioning system described in Japanese Patent Publication No.  2007-85673 below, there is proposed a method of causing the outdoor units to operate one unit at a time, identifying the indoor units whose state quantities change at that time, and detecting that that outdoor unit and those indoor units are in the same refrigerant system.