Abstract: An air conditioner includes an outdoor unit, a plurality of mode change devices including at least one mode changer including a branch duct and a changing valve, and configured to receive a control signal from the outdoor unit to control an operation of the at least one mode changer. A plurality of indoor units are connected to the outdoor unit or the plurality of mode change devices. The outdoor unit may determine an operation mode to operate the plurality of mode change devices a plurality of times. Each of the plurality of indoor units may detect a temperature change of an indoor heat exchanger in response to the operation of the mode change devices, to determine the number of connected mode changers and a connectable mode changer candidate group based on the temperature change of the indoor heat exchanger.