Honeywell RTH8580WF Wiring

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Old 08-06-13, 09:18 AM
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Honeywell RTH8580WF Wiring (No C-Wire Connection)

Hello, folks.

The short and sweet of my post is Im looking for some help hooking up a new Honeywell RTH8580WF (replacing a Honeywell RTH230B) to a Trane air handler, model 2TEH3F42B1000AA. I don't know if it's relevant, but the outdoor unit is a Trane XR13.

I recently picked up a digital Honeywell RTH8580WF WiFi thermostat to replace a currently installed digital Honeywell RTH230B thermostat. The current RTH230B thermostat is digital, however, it is battery powered and did not require a C wire to power the unit, this new tstat does. I cut the power to the air handler and outdoor unit so I could open up the handler and take a look inside. Now, what I typically see in posts/forums regarding this issue is that there is almost always a free common wire available or a set of terminals conveniently labeled with R,G,Y,W, and C, where all that is required is to connect the C wire to the C terminal and thats that. Unfortunately, that is not the case with the unit Im working with. It appears to just be the individual wires from the tstat cable connected to various loose wires within the air handler. I'd rather not guess and guess wrongly.

Ive taken several high resolution pictures that show the current tstat configuration, the information label on the air handler panel, the wiring diagram for the air handler, the wiring setup upstairs where the lines run into the air handler and to the transformer, the tstat cable from the tstat unit running into the air handler and the respective connections for each individual wire, the wiring running to the fan, and connections from an additional brown tstat cable that runs into the air handler from the wall (which I suspect runs to the outside unit).

Ive taken a little crash course on reading the wiring diagram and can identify the wires and components indicated in the diagram, but Im just at a loss with respect to where to connect the C wire from the tstat cable running from the tstat unit into the air handler and was hoping someone could provide some guidance. The pictures are too large to attach to this post, but here is the link to the high-resolution originals with some descriptions and labeling I've added:

Thermostat Wiring - Imgur
 

Last edited by fz1328; 08-06-13 at 11:01 AM. Reason: Updated outdoor unit model #
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Old 08-06-13, 03:15 PM
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"C" connection is the BLUE wire (from the AHU) that is currently connected to a white wire going to the outdoor unit.
 
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Old 08-06-13, 03:59 PM
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Thank you so much for your prompt reply. Would it simply be a matter of connecting the currently unused C wire running to/from the tstat unit to that same connection you identified in your reply (pictured below), which would result in both the white wire running to the outdoor unit and the currently unused blue C wire being simultaneously connected to the blue wire running from the AHU?

 
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Old 08-06-13, 04:12 PM
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Yes, you said it very well........ That would be sufficient
 
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Old 08-12-13, 01:04 PM
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Hello, can you let me know if this worked? I have the same exact situation. There is no issue or risk in sharing the wires?
 
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Old 08-12-13, 01:06 PM
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hvactechfw was spot on with his advice. I connected the additional wire and it worked flawlessly. Everything is running as it should.
 
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