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Ok, here's the deal. I currently have a zoned system with a fresh air "ventilator" (actually just a fresh air damper) and I want to install an ecobee thermostat. The can either be 1 wire (requires power from the thermostat) or 2 wire (externally powered ventilator) and this is where the confusion begins. On my current thermostat I have two wires going to my fresh air damper, yellow on U1 and white on the C terminal, and if you look at the damper wiring you see the two wires coming from the thermostat and no other external power source. I believe the installer chose to jumper the C wire at the thermostat which is confusing me to have a 2 wire setup when in fact I actually have a 1 wire setup which gets power from the thermostat.... am I confused? enter image description here

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  • Can you post a larger photo of the thermostat wiring? – ThreePhaseEel Oct 26 '17 at 2:59
  • Here is a larger picture of the thermostat, you can see the two wires going to the damper. Notice there are 2 wires connected to the "C" terminal. – Jim R Oct 26 '17 at 3:17
  • So where did you put the U1 wire on your ecobee? Can you post a picture of the final product? Thanks – Harold77839 Jan 10 '18 at 14:38
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Your damper is a 1 wire setup

Basically, your damper is set up as a "1 wire" setup, as that nomenclature assumes that the C wire is returning directly to the air handler transformer, whereas in your configuration, the C wire is returning back to the thermostat first, and then going from there to the air handler transformer. So, simply proceed using the "1 wire" instructions, making sure that both C wires land on the C terminal of the Ecobee.

  • That's what I thought but wasn't sure, I appreciate your quick response and explanation. – Jim R Oct 26 '17 at 3:26
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    @JimR -- we thank people around here by upvoting and/or accepting their answers :) – ThreePhaseEel Oct 26 '17 at 3:31

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