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New Member
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Sep 19, 2008, 04:17 PM
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Furnace Wiring - Adding a common "C" wire
My new thermostat has uses a W,R,Y,G and now a "C". My wiring has only W,R,Y, and G and these are needed.
How do I, or can I add the needed "C" wire? Is it just adding a wire from the transformer? :confused:
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Uber Member
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Sep 19, 2008, 05:06 PM
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(C) depends on the stat. Battery powered ones make (C) an optional connection.
(C) goes to the other terminal of the secondary that (R) does not go to. You should find a few low voltage wires on that terminal (gas valve, fan, and outside AC unit all tied together)
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Ultra Member
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Sep 19, 2008, 06:17 PM
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Originally Posted by Bocaheat
My new thermostat has uses a W,R,Y,G and now a "C". My wiring has only W,R,Y, and G and these are needed.
How do I, or can I add the needed "C" wire? Is it just adding a wire from the transformer? :confused:
Are you saying that you need a fifth wire that runs from the furnace to the thermostat? If so all you have to do is to just add one 18 gage wire to the four that you already have or you can buy a different wire that has six or more wires and replace the four wire cable that you have now.
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New Member
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Sep 20, 2008, 10:05 AM
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Ok. Added the wire but now the Fan will not turn off. I used the "B" terminal for the common. Any ideas what is wrong?
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Uber Member
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Sep 20, 2008, 01:33 PM
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Common may not be marked. There are two wires that go to the outside unit. One is connected to "Y". The other wire will be common.
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Ultra Member
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Sep 20, 2008, 06:05 PM
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Originally Posted by Bocaheat
Ok. Added the wire but now the Fan will not turn off. I used the "B" terminal for the common. Any ideas what is wrong?
Which fan will not turn off? The indoor fan or the outside fan. Let me know and I can tell you what to do.
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New Member
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Sep 30, 2008, 06:59 AM
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Originally Posted by letmetellu
Which fan will not turn off? the indoor fan or the outside fan. Let me know and I can tell you what to do.
Inside fan keeps running. Note, the other side of the Blue wire goes to the same common terminal inside the furnace.
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Uber Member
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Sep 30, 2008, 08:18 AM
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Remove the "G" wire from the thermostat. Does the fan turn off?
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Uber Member
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Sep 30, 2008, 08:26 AM
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Let's make this simple. G,R,Y,G and C
Let's leave C out of this temporarily.
When R connects to G, the fan comes ON.
When R connects to W, the furnace turns on: The furnace controls the fan (On and Off)
When R connects to Y, the outside AC unit comes on.
Thermostat oddities:
In heat, the fan is controlled by the furnace, but Turning the fan to the ON rather than the auto position sometimes doesn't work in heat mode. OFF will not turn off the fan - the furnace must do it.
In cool the thermostat controls both the W and G terminals. In order to get cool, both Y and G are connected to R.
When a common is used, there will be 24 VAC between R and C at all times.
Bold items were corrected thanks to EPM.
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New Member
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Sep 30, 2008, 01:12 PM
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Originally Posted by KeepItSimpleStupid
Let's make this simple. G,R,Y,G and C
Let's leave C out of this temporarily.
When R connects to G, the fan comes ON.
When R connects to Y, the furnace turns on: The furnace controls the fan (On and Off)
When R connects to W, the outside AC unit comes on.
Thermosat oddities:
In heat, the fan is controlled by the furnace, but Turning the fan to the ON rather than the auto position sometimes doesn't work in heat mode. OFF will not turn off the fan - the furnace must do it.
In cool the thermostat controlls both the W and G terminals. In order to get cool, both Y and G are connected to R.
When a common is used, there will be 24 VAC between R and C at all times.
I will try this weekend... I'm on the road. Will let you know how I make out. Appreciate the help. If I can not get it figuredd out, I will include some pictures. Thanks
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Senior Member
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Sep 30, 2008, 04:53 PM
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Originally Posted by KeepItSimpleStupid
Let's make this simple. G,R,Y,G and C
<snip>
When R connects to Y, the furnace turns on: The furnace controls the fan (On and Off)
When R connects to W, the outside AC unit comes on.
<snip>
Uhh... KISS, I think you got it backwards. Unless they do it differently in your part of the world.
R to Y calls the compressor, which usually is cooling. If it is a heat pump then the O or B terminal (the type of reversing valve determines which must be used) decides whether it will heat or cool.
R to W calls heat. If it is a heat pump W often is the second stage (W2) or backup heat.
Some systems control the fan from the control board and some from the thermostat. You program your tstat accordingly if it allows you to. Otherwise R to G will call the fan (you had that correct), and the temp limiters will overide the fan call and keep it running until the system is below the limit switch threshold.
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New Member
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Oct 3, 2008, 02:19 PM
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Ok, here is what I have found. Please see attachment. When I connect the Yellow wire to "C" the fan inside turns on and stays on. (Thermostat - Furnace) RH-R, G-G, W-W1, Y-Blue wire, and finally C-B.
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New Member
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Oct 3, 2008, 02:24 PM
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Sorry, not correct! The "O" and "B" terminal on the Furance are reversed.
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Uber Member
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Oct 3, 2008, 02:33 PM
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Since the new tstat has Rh, there musct also be an Rc. Rc and Rh MUST be jumpered together.
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New Member
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Oct 4, 2008, 03:41 AM
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The instrucion had me insert a jumper for my configuration. I assume that was what it was for.
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Heating & Air Conditioning Expert
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Oct 4, 2008, 03:59 AM
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Unless it was missed can you post the brand and model of your new thermostat?
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New Member
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Oct 4, 2008, 10:51 AM
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Ritetemp 6080
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Heating & Air Conditioning Expert
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Oct 4, 2008, 10:56 AM
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If you follow this all should work. Now if the wiring color has not been followed by the original installer then you might have to track down the wiring and start over.
The RiteTemp Support Site - 6080 Technical Support Page
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New Member
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Oct 4, 2008, 11:00 AM
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I rechecked the wiring and it seem to be working now. Thanks.
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Heating & Air Conditioning Expert
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Oct 4, 2008, 11:07 AM
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Glad you got it going. Keep the web site for future use if necessary.
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