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Author Topic: Do I have a C-wire?  (Read 347 times)

Offline stevebass

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  • Member Since: Jul 2009
  • Posts: 36
Do I have a C-wire?
« on: November 02, 2021, 12:35:16 PM »

I bought a Nest thermostat and it wants a C-wire. There's no C at the thermo, but Nest sells a gizmo to configure a  C wire at the furnace (Payne 395B - 395b060095).

From the images, can anyone tell me which is the C wire? Thanks a bunch!Four images: one is the wiring on the Nest. The other three are in various areas of the furnace (which is ancient).

Offline stevebass

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  • Member Since: Jul 2009
  • Posts: 36
Re: Do I have a C-wire?
« Reply #1 on: November 02, 2021, 04:55:09 PM »
Update: I found the thermostat wire terminal board. A thin brown sheath has a white and red wire. The Red goes to the C terminal. The White goes to Yellow terminal (where there's an existing yellow wire).

So it appears I have a C-wire at the furnace, correct?

What's the function of the white wire attached to the yellow terminal?


Wire Terminal Board



Offline stevebass

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  • Member Since: Jul 2009
  • Posts: 36
Re: Do I have a C-wire?
« Reply #2 on: November 02, 2021, 04:57:43 PM »

Thermostat Wire Terminal

Offline houptee

  • Technician
  • Member Since: Jan 2010
  • Posts: 167
Re: Do I have a C-wire?
« Reply #3 on: December 02, 2021, 07:07:54 AM »
Connect the Blue wire to C at furnace with the Red and go find the Blue at the Thermostat wire and connect to C on Nest.
Looks like you will need to pull the wire out from the wall and maybe strip more brown insulation to access the Blue wire or it might be wrapped around the wire inside the wall.

After you connect it you need to go thru the setup again with the Home app, delete the thermostat and add it again into the app and tell it there is now a C wire connected.