An air conditioner, a control device thereof, and a method of controlling the same are provided. The air conditioner includes a control device including a plurality of indoor unit operation changers, and an indoor unit connected to any one of the plurality of indoor unit operation changers, where at least one of the indoor unit and the control device determines an operation mode of each of the plurality of indoor unit operation changers respectively connected to a plurality of indoor units, detects an indoor unit operation changer at an operation mode corresponding to an operation of any one of the plurality of indoor units among the plurality of indoor unit operation changers, and determines an indoor unit operation changer connected to the indoor unit among the plurality of indoor unit operation changers on based on a result of detecting at least one of the indoor unit operation changers.