Hi all! I am installing an ecobee3 lite thermostat to replace my vanilla thermostat. I noticed the common wire going to my thermostat was not energized, so I traced it down to my furnace's electrical board.
I noticed there are two thermostat wire bundles running to my furnace (see attached photo):
1. The first bundle of wires I can trace back to my thermostat. They are connected to the Y/Y2, W, R, and G ports on the furnace. The Blue 'C' wire has been intentionally snipped and is not connected to C on the furnace (which is what I want.)
2. The second bundle of wires is connected only to the Y/Y2 on my furnace, and the C wire. I tried to trace where these are going, and I am not sure. One potential place is to my AC unit bolted outside my house, but I've yet to confirm that.
I am wondering a few things here:
1. Where is that second pair going to? Pretty high chance its going to my AC unit? If so what are those wires specifically used for?
2. Whether or not its going to my AC unit, is it safe to share that C wire with the bundle that goes to my ecobee thermostat? Since that blue wire was apparently intentionally cut off, I'm afraid to run it in parallel for fear of burning something out on the furnace (unless consensus is that I shouldn't be.)
Thanks for your advice!