Trane C Wire


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Old 04-29-15, 08:31 PM
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Trane C Wire

Working on getting a RTH9580WF installed on my Trane AC/Furnace.
There is a terminal labeled C inside the unit and I have a 8 wire thermostat wire.

So I wired the brown wire to the C terminal and proceeded to hook up the new thermostat and got nothing (no power at stat). Broke out the volt meter and with the furnace door switch activated I tested the C terminal in the furnace and got 0 volts. Went down the line and found 26v at the R terminal. Moved my brown wire down to R, tested voltage at the thermostat brown wire and get 26v at all times. Reconnected the new Honeywell and still nothing. I am suspecting a bad unit, but wanted to see what you guys think before I take this one back. I did take my existing plane jane non programmable Honeywell and connected my 26v brown wire to the C terminal in the stat and did not get power there either (it can take batteries) which has me questioning if its a wiring issue or stat issue.
I expected the C terminal in the furnace to be 24v, but I'm not getting it with my volt meter. The R terminal currently has only a water sensor connected to it. Here are the pictures. This picture was taken before I moved the brown wire from C to R.
Edit to add there is a humidifier w/ its own 24v transformer attached to this unit so you will see a few extra tstat wires.





 

Last edited by tul9033; 04-29-15 at 09:17 PM.
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Old 04-29-15, 09:17 PM
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Welcome to the forums.

R = 24vac
C = common

Between R and C you should measure your 24vac.

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Old 04-29-15, 09:56 PM
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Thanks for the reply. What should I do? If I put the brown wire on C, the only thing on R is the water sensor. Do I jumper C and R? Putting brown on C leaves me with no voltage.
Thanks again
 
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Old 04-29-15, 10:00 PM
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It looks like a black wire from the float switch is connected to the R terminal but the second black wire from the float switch isn't connected to anything?

I would connect stat blue to furnace common, connect stat red to the float switch black wire that isn't connected to anything and connect red and to R at the stat. I would connect blue to C at the stat.

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Old 04-29-15, 11:14 PM
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Thanks for the reply. Could you clarify this part "and connect red and to R at the stat."
Thanks
 
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Old 04-29-15, 11:33 PM
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and connect red and to R at the stat
He meant to say and connect red to R at the stat.

This way you have the float switch connected in series with the 24v to the stat. If you have a pan overflow it'll shut down the stat and you'll know there is a problem.
 
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Old 04-30-15, 05:39 AM
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Thanks PJ, that is what I meant.
 
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Old 04-30-15, 08:51 AM
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Thanks again.
There are 3 tstat wires in the enclosure. 1 to the actual tstat, 1 to the humidistat, and 1 to the outside unit. There is a red wire from the humidistat connecting to the red and yellow thermostat wire connection. Does that change the plan? What's missing from the picture is the outside unit wire. Unfortunately I have to climb an 8 foot ladder and move a 4x6 piece of MDF to gain access to the attic area. I want to have a plan when I get up there. Getting in and out of the area is a task.
I could always use a 24v tansformer I have and run new wires from the transformer to the blue/brown and plug the blue in the thermostat C and brown in the Rc. Of course that still leaves the issue with the float not being connected correctly. This is a new house so to see this omission is a bit concerning. They have already forgotton to purge the nitrogen out of the line keeping the AC from running.
Thanks
 
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Old 04-30-15, 09:54 AM
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Stat Y and one of the 2 condenser wires should be connected to the furnace Y for correct airflow in cool mode.

The remaining condenser wire connects to furnace C along with the stat C wire.
 
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Old 04-30-15, 11:58 AM
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Thanks for all the help. Came home at lunch and got it all taken care of. Nice new wifi stat installed.
 
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Old 04-30-15, 04:14 PM
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Good job.

With the air handler in the attic you definitely want the float switch connected.
 
 

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