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khayman218 07-28-2008 06:57 PM

Missing Common Wire?
I have the following setup for my current battery-operated thermostat.

From the wall, there are four wires:
[Terminal connection on old stat] - Wire Color from Wall
[RH] - RED **
[b] - NONE
[O] - NONE
[Y] - BLUE
[RC] - RED **

**These wires are jumpered together from one red wire from the wall.

I am installing a new one that is not battery operated. I guess I will have to pull up a new common wire for it? What is the best way to find and bring up a new common wire for the new thermostat?


8 Ball 07-28-2008 11:57 PM

Buy a length of small chain, drop one end down the wall from where the existing wire comes out at the stat. You may have to expand the opening in the basement, or wherever the wire comes out. Wrap the new wire through the last link, and pull the new wire to the stat location.

If your air handler is in the attic, drop the chain from the attic opening to the stat.

Sometimes its just easier to pull a new 5 or 6 conductor wire. (6 will give you a spare).

Have fun.

khayman218 07-29-2008 07:09 AM

Thanks for the help!

Will the common wire terminal be on the indoor unit or the outdoor ac unit?

8 Ball 07-29-2008 05:03 PM

At the furnace terminal strip, your condensor, outdoor unit, is connected to Y and C already. From your stat to the furnace terminal strip is where you need to add the C.

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