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Ecobee3 + Taco ZVC404exp + C-Wire = ???

I've spent hours upon hours researching this and am stuck at where to connect my C-Wire at my Taco controller.

At my thermostat I have RWG wires and the green was previously unused. Trying to convert the Green to a C-wire. The problem is my older Taco ZVC404exp does not have a Common terminal as far as I can tell.

Attached are pics of the wiring at the Taco as well as the thermostat? Zone 3 is the the target for this stat.

Suggestions? Thanks



Comments

  • neilc
    neilc Member Posts: 1,654
    overthere on the left where the brown transformer wires land at J4, what's noted on that edge ?
    tone them out(read volts) with a volt tester, between the red Rc you already have landed,
    likely that white wire, or the 1st terminal screw above it,
    or,
    where's the manual for this?
  • zdog2x
    zdog2x Member Posts: 6
    The red and white attached to the terminals near J4 are used to power a Carrier Thermostat for a different part of the house. If I check the voltage between the white (near J4) and the Rc (Zone 3) it show 26VAC.

    I previously connected the Green (Common) to the same location as the white wire at J4, but the Ecobee didn't turn on. Interestingly, that connection triggers the circulator pump for Zone 3.

    No manual for the Taco.
  • neilc
    neilc Member Posts: 1,654
    edited October 2019
    I should have disclaimed,
    I don't do this every day , , ,

    I'm tempted to suggest it should also work at the open Comm where the 120 comes in,
    But I'ld rather a pro here confirm that.
    can't hurt to check with the volt meter , , ,
  • zdog2x
    zdog2x Member Posts: 6
    No problem. Thanks for looking. The modern version of the Taco has a comm for each zone so it would be straightforward.

    I believe the comm at the bottom is 120VAC so I'm steering clear of that one.
  • neilc
    neilc Member Posts: 1,654
    yeah, I'm a blind idiot,
    that comm is DHW relay,
    stay away.
  • HVACNUT
    HVACNUT Member Posts: 4,355
    J4 is designated 24v power in. There are two transformers so theres 24v at the top 2 terminals and 24v at the bottom 2. Looks like the bottom 2 are powering the Carrier thermostat.
    See if those terminals are labeled R-C. If so then C is your common. If they're not labeled, you'll need a meter to check.
    I don't know if it matters with your thermostat but power is at Rc, not Rh which is for heat. Unless its internally jumped?
  • zdog2x
    zdog2x Member Posts: 6
    edited October 2019
    The lower (white) wire at J4 is connected to C at the carrier panel. And the Red to Rc.

    My current wiring (which does not work) is:
    White from thermostat W1 to Taco zone 3
    Red from thermostat to Taco zone 3
    Green from C on thermostat to J4, second nut from bottom.

    In this case the thermostat will not turn on, but Zone 3 turns on and starts delivering heat.

    I *believe* the Ecobee internally jumpers Rc and Rh. I suppose I could do it manually as well.

  • HVACNUT
    HVACNUT Member Posts: 4,355
    Connect your green to a J4 common. Switch the red and white wires at TT for zone 3. Move red wire on the Ecobee to Rh.
  • Does it matter which transformer provides power?
    Often wrong, never in doubt.
  • HVACNUT
    HVACNUT Member Posts: 4,355
    > @Alan (California Radiant) Forbes said:
    > Does it matter which transformer provides power?

    To a point. 2 zones per transformer. On the newer revisions, the 4 zone board has one 40va transformer. They bump up to two with the 6 zone board.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,425
    Ecobee needs red on Rc not Rh for heat only applications.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    HVACNUT
  • Someone should make a YouTube video on this as it comes up often.

    This one doesn't seem to work for me:
    Often wrong, never in doubt.
  • hot_rod
    hot_rod Member Posts: 15,413
    at some point it may be less frustration to replace the relay with one that makes 3 wire stats easy to install. Shouldn’t need to customize inside the relay box https://www.caleffi.com/usa/en-us/catalogue/z-onetm-relay-multi-zone-zsr103
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • zdog2x
    zdog2x Member Posts: 6
    Thanks to everyone for the responses.

    I'll try the recommendations of HVACNUT and Robert when I get home on Wed.

    I actually saw that video Alan sent and it's what prompted me to use the terminal near J4 for the common. And agree that just replacing the whole setup is the best solution - I've got seven zones and haven't come across a controller that does more than 6.
  • HVACNUT
    HVACNUT Member Posts: 4,355
    > @zdog2x said:
    > I've got seven zones and haven't come across a controller that does more than 6.

    But there are expandable relays.
  • zdog2x
    zdog2x Member Posts: 6
    Update:
    HVACNUT said:

    Connect your green to a J4 common. Switch the red and white wires at TT for zone 3. Move red wire on the Ecobee to Rh.

    I did this except I left the red on the Rc at the Ecobee - see first pic below. Ecobee did not activate and nothing happened at the relay. Note Green Common attached to J4.


    Next, I left the Common at J4 and switched the Zone 3 back (second pic below). In this case the Ecobee does *not* turn on, but Zone 3 is triggered at the relay (lights at right side of pic and heat delivered to zone).


    Lastly, with the wiring as shown in the second pic, I checked the voltage at the Ecobee.
    R<-->G = 26V
    R<-->W = 26V
    W<--G> = 0V

    Bad Ecobee? Any way to just test it to see if it powers up?

    Thx
  • hot_rod
    hot_rod Member Posts: 15,413
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 15,413
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream