You may know the Jackson Five hit that line comes from.
(The first time I heard it was NOT on an oldies radio station.) Unfortunately, when it comes to communicating controls, one bad communicating board CAN take down the whole network. If the communicating portion of a board is sufficiently damaged, it can prevent communication to ANY of the components on the communicating network. This is because they are all tied together in parallel. A sufficiently low resistance can pull down all communication signals on the whole bus. We saw this first hand this week in our lab. A system that had been operating correctly started having problems communicating. A lab instructor had put in a problem and the student tried to troubleshoot by swapping wires around, resulting in a dead board. (In my experience, swapping around wires just to see what will happen almost never ends well!) Now, the ENTIRE SYSTEM stopped communicating and the control could not find the furnace, which did not have any problems. When the communicating wires to the condensing unit were disconnected, the thermostat found the furnace and was able to operate it. The bad condensing unit board managed to pull down the entire communication bus. When you have a communicating control system that will not communicate, the first step should always be to check your connections. Make sure they are correct and making good contact. Then, try to isolate different parts of the system by connecting one part of the system at a time to the communication bus and seeing which specific component will not communicate. Unlike standard 24 volt controls, you cannot read a voltage to determine if a board is communicating. Isolating the components and checking them individually usually identifies the component which is causing the problem.