An air conditioning system includes: an outdoor unit of an air conditioner; an indoor unit of the air conditioner; and a remote controller that operates and monitors at least one of the outdoor unit or the indoor unit. The remote controller includes: a storage and a processor coupled to the storage. The processor of the remote controller: acquires operation data from at least one of the outdoor unit or the indoor unit; stores the operation data in the storage by overwriting pre-stored operation data already in the storage when a predetermined capacity of the storage is exceeded; saves, during a past predetermined period when an abnormal condition occurs at the air conditioner and in the storage, a copy of the operation data; and displays the copy of the operation data or sends the copy of the operation data externally.