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Old 05-06-2013, 11:30 AM   #1
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


Hey everyone. As the title says I want to install Nest and I do not have a C wire currently.
I want to install a C wire but I need to get some advice.

I believe I will be able to pull a new wire without problems down to the furnace from the thermostat. I was going to get an 18/5 wire. My question is where does this wire connect to the ac/heating unit? I have an album of pictures here of what I could find.

http://imgur.com/a/iUmoB

I do know that for Nest the jumper from Rh to Rc is not needed and I can connect that wire to either one.

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Old 05-06-2013, 12:10 PM   #2
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


on the circuit board attached to the furnace fan there is a C terminal on that board. need to lay down and carefully move the wires a bit but it is behind them on that board. 18/6 is available, have never seen 18/5. may be able to buy 18/6 LVT wire at HDepot. sometimes it is stapled to the wall/studs inside your house under the tstat so you may have a hard time or need to use a fish tape or get an electrician to do it.

if it is a Goodman furnace and has no C terminal on the board you may have to find the white C wire from the transformer (low voltage side of it) and connect it with a wire nut as Goodman had some units w/o terminal strips or they did the wiring in the air with wire nuts. 99% sure you can hook it up to that board. then one I saw had a smaller different board with no terminal strips.

Good Luck

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Old 05-06-2013, 12:35 PM   #3
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


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on the circuit board attached to the furnace fan there is a C terminal on that board. need to lay down and carefully move the wires a bit but it is behind them on that board. 18/6 is available, have never seen 18/5. may be able to buy 18/6 LVT wire at HDepot. sometimes it is stapled to the wall/studs inside your house under the tstat so you may have a hard time or need to use a fish tape or get an electrician to do it.

if it is a Goodman furnace and has no C terminal on the board you may have to find the white C wire from the transformer (low voltage side of it) and connect it with a wire nut as Goodman had some units w/o terminal strips or they did the wiring in the air with wire nuts. 99% sure you can hook it up to that board. then one I saw had a smaller different board with no terminal strips.

Good Luck
Where do you mean on the board?
Which arrow is the direction you are talking about?

http://i.imgur.com/3ecjg57.jpg
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Old 05-06-2013, 12:51 PM   #4
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


#1 is it a Goodman furnace?

On the green board if you look carefully at the top there is a G and W terminal with wires on them. there may be a C terminal somewhere on the board that I cannot see. There is also the transformer above the board and there should be 2 wires to it, black and white that are 110 volts high voltage, then there are 2 low voltage wires, Red and C/common. you can wire nut your C to that white/C wire if the board has no C terminal. In your case it looks like the blue from that transformer is C and Red is R/hot. usually they use white instead of blue but it is what it is.
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Old 05-06-2013, 01:02 PM   #5
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


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#1 is it a Goodman furnace?

On the green board if you look carefully at the top there is a G and W terminal with wires on them. there may be a C terminal somewhere on the board that I cannot see. There is also the transformer above the board and there should be 2 wires to it, black and white that are 110 volts high voltage, then there are 2 low voltage wires, Red and C/common. you can wire nut your C to that white/C wire if the board has no C terminal. In your case it looks like the blue from that transformer is C and Red is R/hot. usually they use white instead of blue but it is what it is.
On the outside it Janitrol
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Old 05-06-2013, 01:05 PM   #6
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


Goodman bought Janitrol and yeah it has no C on the board so you need to wire nut it to the blue wire from the transformer. HDepot has wire nuts/Marettes. That furnace is/was prone to heat exchanger failures/cracks/compression rings popping so you should get it checked by a Pro. Make sure the screws holding that bracket to the fan that the board sits on are very tight or add a couple sheet metal screws to it. If it comes loose the board loses its grounding and can blow.
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Old 05-06-2013, 01:35 PM   #7
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


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Goodman bought Janitrol and yeah it has no C on the board so you need to wire nut it to the blue wire from the transformer. HDepot has wire nuts/Marettes. That furnace is/was prone to heat exchanger failures/cracks/compression rings popping so you should get it checked by a Pro. Make sure the screws holding that bracket to the fan that the board sits on are very tight or add a couple sheet metal screws to it. If it comes loose the board loses its grounding and can blow.
So is one of the blue wires on the right the one you are talking about?
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Old 05-06-2013, 01:50 PM   #8
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


Yes, by the Pink arrow. Good Pics w/o them this would not get done. Would be nice if everyone posted them. we get some REAL dumb people here that don't want to co-operate.
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Old 05-07-2013, 10:10 PM   #9
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


Its a goodman that uses ground as common. Connect your C wire to any sheet metal screw with good metal contact.
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Old 05-08-2013, 09:25 PM   #10
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


take it off that powder blue wire on the secondary of the control transformer that is the C the red is the R..stay away from the Rc-Rh on the stat the jump is installed so the cooling and heating use the same R of that TR..so from the C -TR up to the C on the subbase of the stat...note if you hook the C to Rc-Rh it is a dead short....don't use the grounded idea for C catch that wire....if your in the cooling season just borrow the heatng W wire for now...
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Old 05-08-2013, 10:15 PM   #11
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Installing Nest thermostat. Do not have C wire. Want to run new wire.


You can also install a 24vAC transformer and go that route, to supply power for the C wire. Connect one wire from the transformer to Rh & the other to C. Rh & Rc should be jumpered on the thermostat. The transformer does not have to be right where the thermostat is, but keep in mind, that the longer the run, the less chance of having the full 24 volts.

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