# thermostat wiring



## jajiboy (Aug 5, 2017)

I would like to install a smart wifi home thermostat. I need a c wire which I do not see behind my thermostat. I checked my furnace and it has a c wire coming out of it. Here are some pictures. Any help would be appreciated. I have little to basically no knowledge of wiring and electrical stuff so any help would be appreciated.


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## Confounded Also (Aug 19, 2015)

I see two brown cables and the red from the second one goes to the 'C' terminal with the white going to 'Y'.

Where does that second brown cable go? Have you pulled the existing T-stat to see if the second cable is stuffed into the wall, unused?

The diagram mentions an 'Outdoor Unit'. Do you have one? Probably an air conditioner unit.

You can blow those control boards and modules fairly easily, so if you don't know, it may be best to have someone come in and look.


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## jajiboy (Aug 5, 2017)

the brown wire goes up to the top part of the furnace. yes the outdoor unit is a AC unit. I pulled the thermostat off the wall and didn't see anything tucked away. There is a brown wire that comes out of the wall and splits off into the 4 wires you see in the pictures


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## SABL (Jul 4, 2008)

What brand and model number thermostat are you planning to install?? 

The brown 'wire' is the basic cable that has 4 conductors from what I see.


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## jajiboy (Aug 5, 2017)

Honeywell
Wi-Fi Smart Thermostat

Model # RTH9580WF Internet #203926327


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## SABL (Jul 4, 2008)

Maybe these instructions will help. I have always had a 'standard' thermostat but do have the manual fan control which can be used as a 'C' wire. I really haven't looked lately but I'm sure I have a 6-conductor wire running to my thermostat.....pretty much covered if I need a 'C' wire. If not, I can fish a new wire easily......I have a single story house.



> If your current thermostat cable does not provide any extra, unused conductors, you can opt, as we did, to use the fan wire as the C wire. In doing this however, you sacrifice the ability to turn the circulating fan on and off manually at the thermostat.
> Identify the fan wire at the old thermostat, and note its color. It’s usually the one connected to the G terminal.
> Now, go to the heating / cooling system, and locate that same wire inside at the thermostat wiring block.
> Disconnect that wire from the G or FAN terminal, and connect it to the C terminal.


Honeywell Smart Thermostat Wiring Instructions RTH9580WF | Tom's Tek Stop


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## Confounded Also (Aug 19, 2015)

SABL said:


> If not, I can fish a new wire easily......I have a single story house.



In many cases that may not be the worst or most complicated option. T-Stat wiring in a variety of conductor counts is commonly available and is usually quite easy to replace.


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## SABL (Jul 4, 2008)

Confounded Also said:


> In many cases that may not be the worst or most complicated option. T-Stat wiring in a variety of conductor counts is commonly available and is usually quite easy to replace.


T-stat wire pretty easy unless it's not a vertical drop. Depends on where furnace is and T-stat is.....and if it's stapled down. Just tie the new wire onto the old and pull the new in as you pull the old out......make sure the new one is tied onto the old pretty good.


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