I'd like to install an ecobee3 thermostat, but I'm not entirely sure about my wiring. The current thermostat seems to only have a W and RC wire coming into it.
There is also what appears to be a blue wire buried in the wall, but I haven't tested to see if it's a live C wire. I've had an HVAC person out here before, and he told me we didn't have a C wire, so presumably this is something else.
On my furnace, I have two Honeywell R845A boxes, and also an RA832A box. Not sure if this is standard or not, or what exactly it means. I'm hoping it means running a C wire from the furnace, if I need to run it, will be easy.
I also have a weird bundle of wires above one of the two R845As, as follows:
There seems to also be a green wire merged here, about which I'm not sure at all what it does since it doesn't seem to come out of wall upstairs.
My question is: can anyone estimate how difficult/expensive it would be to convert this to a unit that could support a thermostat like the ecobee3 or Nest that need a C wire? (I know some of these power steal and don't need a C wire per se, but I'd rather go the most reliable route here.)
Many thanks in advance for any insights.
EDIT: Opened up the transformer box, and the blue wire is indeed there. But it is snipped off/not connected. Is it just a matter of stripping the wire, connecting an extension, and hooking it up? What do I connect it to? And what sort of wire should I use for the connection? (Picture below.)