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potentially-twinned furnace install

shabermanshaberman NEMember


I have two Trane XR95s, with separate thermostats (main-level and upstairs). I have two Ecobee3s that I thought would be an easy install, although I do need to use the PEK.

However, I opened up the furnaces and they seem semi-twinned? Not actually twinned, I assume, because each one has it's own thermostat, but the C (red)/Y (white) in this one:

Is, AFAICT, hooked up to the C (write)/TWIN (red) on this one:

And so the furnace with the TWIN wired up has what I assume is the Y wire also wired into the TWIN terminal, so I couldn't go through the PEK instructions, which assume a normal Y wire.

I had already scheduled a tech to come by later this week and do annual maintenance + check my work, thinking I'd have it installed by then, but now I'm going to hold off.

However, I'm curious, just so that I know more when the tech comes out, is there an obvious reason why my furnaces would be connected like this? Can I setup two ecobees/PEKs with this wiring?

Apologies if I should submit this to Ecobee support instead; just let me know if that's a better avenue for questions like this.


  • kevinmcckevinmcc Macomb, ILMember

    I am confused by the wiring. One furnace has wires on TWIN, the other does not. According to the manual in a TWIN configuration there is a wire from TWIN to TWIN.

    Was the Red and Yellow meant to be on Y and not TWIN?


  • shabermanshaberman NEMember

    Hm. Interesting theory about red/yellow supposed to go into Y...

    I do have two conventional A/Cs outside, one per furnace...

    I'm wondering if this is basically twin wiring for the A/Cs...e.g. it is the smaller/upstairs furnace/thermostat that was the regular Y wiring (first picture), so if it would decide when to turn the A/C on (which makes sense for the upstairs to decide cooling in the summer), then with its Y on, it's also implicitly telling the larger/main-level unit to turn on it's blower, and then maybe there is another wire that hooks the 1st/smaller unit's Y up to the 2nd/larger unit's AC...

    Dunno, just a wild/naive guess.

    I'm assuming the easiest thing to do, in terms of getting the two ecobees installed, would be to just undo whatever the current wiring is attempting to accomplish...

  • shabermanshaberman NEMember

    Turns out this was just a wiring mistake made at installation (4 years ago); the red/white were to each AC, not interconnected (my naive assumption), and the two yellow/red wires going into the TWIN should have been into the Y.

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