What part of the HVAC system generates the serial?

[xenoxaos]

I just got a new Amana system installed, and it ended up taking way to long for the installer to get the Communicating Thermostat working (It was hot AF in the house) so I just had them set it up in dumb mode with my old zwave thermostat. I figured it was probably some kind of RS485 protocol but quick searches while they were here didn't show me anything. I just came across the project while playing with the CTK04AE powering it from my bench supply and probing around with my scope. I didn't see any traffic on either of the data lines. Do you know what part of the HVAC system does the serial probing? Thermostat? Air Handler? Compressor/AC unit?

[kpishere]

Well, they all do. Initially when turned on. For it to work though, your thermostat will 'win' the coordinator arbitration. You should see regular activity after that. Note that RS485 is differential pair communication. You'll need a scope and can do poor mans differential probing with two probes and the math function and no use of ground. Check out the wiki page in this repo for some screenshots of wiring and devices used.