A method for operating an air conditioner includes transmitting a plurality of signals between a remote user interface and the air conditioner through a plurality of wires that extend between the remote user interface and the air conditioner when the air conditioner is in a diagnostic mode. Each signal of the plurality of signals corresponds to a respective one of the plurality of wires. The method also include sequentially presenting a respective one or more characters on a display of a user interface of the air conditioner in response to each signal of the plurality of signals being received at the air conditioner.