I have an Ultra-Zone EWC-ST-2E controller unit for my gas AC unit at home (heating and cooling). It is set for two zones. Where the first zone has to be on (heating or cooling) in order to enable to operation of the second zone.

Both zones have Honeywell TH3110D1008 thermostats with the following pins: W, Y, G, O Rc, R, B, C

The first zone has the following wires in: W, Y, G, O, R, B The second zone has the following wires: W, Y, G, O, Rc

Is a Nest 3rd generation thermostat compatible with this setup/system?

Below are images of the main AC controller diagram and snapshot, as well as wiring of both zones.

Lastly, can anyone also explain what are the different wires for/meaning?

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Here are more pictures of a pump or so that sits on teh floor next to the heaitng/cooling unit: enter image description here

Here is a picture of the inside of the heating/cooling unit: enter image description here

The bottom part has this controller unit: enter image description here

  • Have you contacted Nest, or checked their online help? Nest maintains a fairly extensive list of compatible equipment.
    – Tester101
    Jul 1, 2016 at 21:30
  • Can you post some higher quality photos of the zone controller, and zone controller paperwork?
    – Tester101
    Jul 1, 2016 at 21:35
  • 1
    R - 24VAC. W - Heat call. Y - Cool call. G - Fan. O - Heat pump changeover (cooling). B - Heat pump changeover (heating). C - Common (24 VAC).
    – Tester101
    Jul 1, 2016 at 22:05
  • Thanks for the letters breakdown. I have added higher res images. Jul 1, 2016 at 22:43
  • I'm not sure why the O and B wires are used with the zone1 thermostat, it doesn't appear you have a heat pump. Is the thermostat set up for a heat pump, or for a gas furnace with air conditioner?
    – Tester101
    Jul 1, 2016 at 23:23


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