Like so many others, I am looking to install a new wifi thermostat with an older furnace. I've searched across the Internet and I have a pretty good idea of what is needed and why; however, I have a couple of questions and I'm hoping someone out there will recognize my setup and provide some clarification. Please note that I purchase this house in 2017, so I was not around for the current furnace or thermostat installation.
So, with regard to the photos below:
Why is the "Y wire" connected to the "Y" port on the thermostat, but the "Com" (C) port on the furnace? Shouldn't it match "Y" <-> "Y"? (Note: You can't see it on the photo, but the yellow wire is twisted so that it connects to the "COM" port on the furnace, along with the red and white wires from the other cable.)
I see that there are extra wires that are unused (blue, orange, and brown). Should I just connect one of those to the "COM" (C) port on the furnace along with the other wire that is there?
So, I guess I'm just wanting to confirm the best/easiest way to create a "C" wire for my new thermostat. My guess is that I use one of the extra wires that aren't being used and just connect it to the "COM" (C) port on the furnace panel, correct?