Honeywell t8400c->Nest E no power

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Old 10-18-20, 09:49 AM
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Honeywell t8400c->Nest E no power

Hello,

I have another thread on fixing my current 4 zone system. We are still working on this. In the meantime I also want to replace the old honeywell t8400c thermostats in 4 locations in the house with these nest E thermostats.

I want to do this as if i want to turn the heat up in the home or in a couple of zones I am running up and down stairs for example and would like that I can do this for one or all possibly through our smart devices or even my phone. Also, i want to be able to set a schedule when they turn down and up.

I checked compatibility and it seems the nest should work but when I connect it the power on the unit does not come on at all. No lights what so ever.

The wires that are on the honeywell were W, Y, G, R so I did the same on the nest.

Any ideas how to get this to work?

Thanks.
 
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Old 10-18-20, 10:17 AM
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With Nests and zoning you normally need a C wire to provide power. If you don't have an extra wire then you can re-purpose the G wire for C without losing much functionality.
 
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Old 10-18-20, 10:24 AM
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I agree with Astuff.
Post the model number of the zoning board.
 
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Old 10-18-20, 10:25 AM
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Thanks for the reply. I want to put one on each zone is my plan.

Can you explain what you mean by repurpose? Also, i do see on the one thermostat i took apart to try this a blue wire that is not used it seems. Could i use this? If so, what do i do at the furnace level to accommodate? (guessing it is here i would need to add the blue wire)
 
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Old 10-18-20, 10:31 AM
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Sorry PJmax we were commenting the same time. I believe the zoning board is a trolatemp mabs ez-4
 
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Old 10-18-20, 10:48 AM
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With that controller..... M1 is shown as a C supply for the thermostat.

 
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Old 10-18-20, 10:55 AM
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I am not sure if this is connected. let me include a picture as well. Should i connect this blue wire at the controller?

 
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Old 10-18-20, 11:01 AM
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Yes.... connect each blue wire to its own M1.
That looks like it will be two wires on each M1. Blue and a white.
 
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Old 10-18-20, 11:28 AM
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ok thanks. I do have a few followup questions.

The 4 blue bars across the bottom is that zone 1, 2, 3, 4 from left to right?
A few questions
1. Any idea why on bar to green looks to be hooked up (right side of that blue bar) but I don't see it used any place else/
2. On the 2 blue bars on the far right, there are a few wires wire nutted together and it is using the blue wire?

 
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Old 10-18-20, 11:35 AM
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The M terminals and wires are the damper motor wires.
There may be different dampers used requiring different wiring.

If they are using a blue thermostat wire.... you need to go to that thermostat and see what terminal it's connected to.
 
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Old 10-18-20, 11:40 AM
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ok. let me do one at a time and i will report back.
 
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Old 10-18-20, 01:37 PM
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Here is what I did at the zone control. Is that correct? It is the blue bar on the bottom. I added the blue war with the white.

What do i connect the blue where to at the nest?


 
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Old 10-18-20, 02:24 PM
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Connect it to C at the nest. Is that not what we were discussing ?

I'm noticing zone 3 has an 8 conductor cable. Something going on with black and blue.
Possibly a humidifier.
 
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Old 10-18-20, 02:32 PM
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I am sorry I totally missed that. Sorry. C at the thermostat. The unit came on now but needs to charge it seems so that is a good sign.

Yes there is a humidifier attached to the furnace. Let me see if i can follow those wires back to confirm. Will i do anything different with that zone wiring wise?
 
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