Where can I get my "C" wire common from?


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Old 10-03-14, 05:32 PM
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Exclamation Where can I get my "C" wire common from?

Hello,

I'm sorry to be asking the same question that has been asked so many times, but it seems everyone has different equipment from me so I'm having trouble figuring this out.

I have oil/baseboard heat, and a Trane Central air unit outside, with a Trane Air handler in the attic.

This is the picture of my current thermostat wiring. I'm installing a Honeywell RTH6500WF (Wifi).

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This is a picture of the wiring on my air handler in the attic.

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My new thermostat wiring has K,Y2, W2,G, W, C, Y, R, Rc

Can you please let me know which wires to put where?

If I put a multimeter on Rh and W, I get 25.X volts so I was thinking of jumping W to C on the thermostat, but I don't want to hurt anything so I figured I would ask someone with more knowledge on this.

My best,
Ryan
 
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Old 10-03-14, 06:42 PM
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Trane's B terminal is 24 volt common (C).
 
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Old 10-03-14, 07:20 PM
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You'll need to be careful here. Does your old thermostat control heat and A/C ?

If not where does the blue wire go and connect to ?
If this thermostat does control heat and A/C then the white on your thermostat is NOT the same white wire that connects to the air handler.

Don't make any changes until we have all the variables ironed out.
 
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Old 10-03-14, 07:49 PM
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Thank you both for the quick replies. PJ, I believe you are correct because the white wire is a different gauge at both locations (at least my eye says so)

My current thermostat does control Heat (oil furnace in basement) and AC (Compressor outside, air handler in attic).
 
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Old 10-03-14, 07:55 PM
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I'd take a look at the wire connections in the attic but I would expect something like this...

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Old 10-03-14, 08:12 PM
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If you find the wire connections like that and you do not have an extra conductor, you can re-purpose the green wire at both ends...

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Old 10-03-14, 08:51 PM
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Thank you the diagram is very helpful.

So if I do find my wiring to be how you showed it in the first diagram, the changes I have to make are:
1. Join G and B at the air handler
2. Bypass air handler with the Y wire from the thermostat to the condenser

Will this make it so the fan is always ON with a/c or always on AUTO?
 
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Old 10-03-14, 08:58 PM
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1. Join G and B at the air handler
No. Move the green wire to the B terminal at the air handler along with the white wire from the condenser that is already there.
The stat end of the green wire moves from G to C.

2. Bypass air handler with the Y wire from the thermostat to the condenser
No, the Y wire is bypassing the air handler now but we want the stat Y on the air handler G terminal. The condenser Y wire also connects to the air handler G terminal.

Will this make it so the fan is always ON with a/c or always on AUTO?
The fan will always be on Auto. You will lose the ability to always have the Fan On.
 
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Old 10-10-14, 07:57 PM
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Thank you Sir!

I was able to get this thermostat working per your instructions. My wires were different colors but with some ohming and many trips from attic to condenser/thermostat/etc I was able to draw my wiring and use that to figure out how and where to move and add wire.

Appreciate your time helping me out!

My best,
Ryan
 
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Old 10-10-14, 10:38 PM
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Thanks for stopping back. Appreciate the feedback.
 
 

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