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I apologize in advance if this is not the correct forum for this. If so, please let me know where I should start.

I am looking to have my central heat pump set up with Ecobee Enhanced. For background, the system has heat and A/C as well as aux heat. There are only two wires being used on the current thermostat, see attached.

I worked with Ecobee support for a few hours and they stated that it may be possible as it appears the hardware needed is present, but would require a technician to do some additional wiring. I tried using their service to locate a contractor in my area, but there are none. I think this is something I may be able to do myself, but I just need to understand what I need to do exactly. All wiring is exposed and accessible and I have the tools to strip, crimp, etc. I was also provided a diagram from them which you can see attached as well. Note: I noticed 2 extra wires in the wall.

Any and all help is appreciated! Thank you.

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  • Can you post the wiring diagram of your heat pump's indoor unit please? Something weird is going on here... Nov 17, 2023 at 3:13
  • Not sure about that model, but some smart thermostats can work with an (extra cost) adapter that combines power and communication into just two wires, letting you use the existing two-wire connection to the thermostat and split it up at the HVAC equipment. I just pulled new wire.
    – keshlam
    Nov 17, 2023 at 3:22
  • I'm having zero luck finding the install manual for your heat pump. It's got two wire comms which you will have to switch to standard 24v comms to use with an ecobee3. The wiring instructions should be in the installation manual for the heat pump.
    – KMJ
    Nov 17, 2023 at 5:01
  • Thanks all for looking into this. I have added 4 pictures I found in the manual in relation to wiring. @ThreePhaseEel
    – Zach
    Nov 17, 2023 at 13:00
  • What is it you need help with? Pulling new cable from the heat pump to the 'stat location? Connecting the wires at each end? Something else? Not really all that clear from your question - after all, there isn't a single question mark in your entire post... It would be a waste of time if someone were to write up an answer telling you how to pull wire if you already know how to do that...
    – FreeMan
    Nov 17, 2023 at 13:15

1 Answer 1

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You'll need to pull a new cable

Your old wired controller communicated with the indoor unit over a proprietary two-wire interface. As a result, you'll need to completely redo the wiring in order to install your Ecobee; the only good news is that your indoor unit does support a 24VAC thermostat interface, according to the manual pages you posted.

I'd use an 18/8 cable at a minimum for this, unless your existing thermostat cable has enough wires in it already; this provides enough wires for a C-wire from your indoor unit, as well as for two-stage control if your system supports it. Once you have that in place, follow connection method B in your manual and match the labels up with your thermostat's: W1 to W1, Y1 to Y1, G to G, R to Rh or Rc, C to C, and B to O/B.

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  • Thanks! I assumed this as well. I picked up the 18/8 cable and now have it in place, but am still unsure of which wires I should be using and where on both the indoor unit and thermostat itself. Which diagram should I be referencing above? Apologies, this is sort of a ELI5 situation.
    – Zach
    Nov 18, 2023 at 12:28
  • That's how my Bryant heat pump is set up - with a Bryant supplied T-stat and a 2-wire interface. I found out the hard way when I tried to install a donated Nest T-stat.
    – SteveSh
    Nov 18, 2023 at 15:20
  • Note to OP. There are 3rd party options out there (may require some hacking skills) that convert from a smart T-stat n-wire interface to the proprietary 2-wire serial protocol.
    – SteveSh
    Nov 18, 2023 at 15:23
  • @SteveSh, did you end up getting yours to work? If so, did you end up having to rewire with 18/8? If so, which wires did you end up using?
    – Zach
    Nov 18, 2023 at 21:45
  • @Zach - This was my son that did this, not me. He already had the 18/6 (or 18/8, whatever) running through the walls. When he had the Bryant system installed, they just used a couple of the existing wires in the cable, but left the remaining ones there, intact.
    – SteveSh
    Nov 18, 2023 at 22:22

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