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Install WiFi Honeywell T-Stat with no C Wire on Separate Furnace/AC

Install WiFi Honeywell T-Stat with no C Wire on Separate Furnace/AC

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  #1  
Old 12-18-14, 09:59 AM
S
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Install WiFi Honeywell T-Stat with no C Wire on Separate Furnace/AC

I've been while digging through tons of posts hoping I can find the answer on my own, but I'm very new to this stuff so could use the help of some kind experts out there.

Here's the situation: I have a new WiFi Honeywell that needs a C-wire but I currently have a 5-wire T-stat (W, RH, RC, G, Y) with no C. My old T-stat:

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Running new wire is going to be very difficult, and I don't care about losing manual fan control, so I'd like to repurpose the T-stat G wire and then jump Y and G at the control board. This seems to be the recommended "hack".

I have a hydronic furnace and a Trane 4TEExxx model air handler. I don't think I need to do anything at the furnace, but the wiring at the furnace has me confused because I see a C, Y, G, etc. terminals.

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The Trane air handler has no C terminal but in looking at the schematics the "B" wire is the common.

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Am I reading that correctly? So what I'm thinking I can do is:

(Turn off all power)
1. Don't do anything at the furnace.
2. On the Trane air handler, move the G wire to the B terminal.
3. Jump Y to G.
4. At the T-stat, hook up the C to the previous G wire.
(Turn on all power)

Would that work? Outside of running new wire, is there a better way to handle this? Really appreciate any help on this as I've been struggling mightily with this. Thanks!

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  #2  
Old 12-18-14, 11:42 AM
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Welcome to the forum!! Yes, you should be able to wire it as you propose. A Trane/American Standard system is different from others as the B terminal is the common. Make sure you turn off power to the air handler and the hydronic furnace before moving the wires. I suggest you try the set-up on your old stat before wiring up the new one. On your new stat don't forget to remove the jumper between R and RH before wiring it up.
 
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Old 12-18-14, 12:39 PM
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Thanks for the feedback firedawgsatx! Unfortunately I won't be able to test whether the wiring will work on the AC side since it's in the 30's around here, so as long as the new thermostat powers up and controls the heat properly then I'll be good for now.
 
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Old 12-18-14, 01:17 PM
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Another possible solution: It appears you have an unused green wire at your thermostat. If you find that green wire at the other end at your hydronic furnace you can run a wire from there to the B terminal on your Trane terminal board. Then connect that green wire to the C terminal on the thermostat. That would allow you to retain normal control of your blower and power the new thermostat.
 
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