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BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22110
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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So I have a Bryant Evolution thermostat with the wires

Customer Question

So I have a Bryant Evolution thermostat with the wires A-green, B-yellow, C-White, and D-Red, along with an unused Blue wire in the back of my thermostat. I want to install a NEST but I don't think it will work. Does anyone have any insight to this being possible?
Submitted: 7 months ago.
Category: HVAC
Expert:  BillyHvac replied 7 months ago.
Hello, My name is Billy. It will not work. Your existing thermostat is a "communicating" thermostat just for your system. It is not interchangeable with the nest. Some units are capable of being converted but it would require rewiring at furnace, thermostat and possibly ac. But as it stands it will not work, Billy
Customer: replied 7 months ago.
I would like to know how to rewire this at the furnace if possible. Is there a diagram I can follow to allow me to rewire it. I assume it would only use 5 wires to accomplish a reconnection. If that is the case I would like to know how to do it.
Customer: replied 7 months ago.
Had I known I was going to get a proprietary piece of shit wiring interconnection that limits the types of thermostats I would have never agreed to use this device.Marc
Expert:  BillyHvac replied 7 months ago.
The current thermostat "talks" to the system in a regular exchange of information.Fan speed, burners, ac.....it operates the system at its highest efficiency possible. Problem is when you want to change thermostats it does 2 things.. Requires new wiring...and also lowers efficiency.If you supply the furnace model number or take pic of circuit board in furnace I can see if yours can be converted to standard 24v off/on use instead of the communicating operation. Billy
Customer: replied 7 months ago.
Thanks Billy, can I just buy another circuit board that would allow me to use a NEST.
Expert:  BillyHvac replied 7 months ago.
you may not need to change. Once I see the board or you give me model number I can see if you have the alternate terminals.
Customer: replied 7 months ago.
Here are some pictures ..let me know if I am in the proper area or not.
Customer: replied 7 months ago.
Here are two more from the furnace. I am not sure where the circuit board you need to see is located.
Expert:  BillyHvac replied 7 months ago.
behind the bottom metal panel that has the peep hole in it. That peep hole is see the board diagnostic light. You would need to remove the bottom panel
Customer: replied 7 months ago.
Thanks Billy I will do that in the am.
Customer: replied 7 months ago.
OK so I was up early and took the unit apart to get to the circuit board. Here are two pictures.
Customer: replied 7 months ago.
Please do let me know your thoughts.
Expert:  BillyHvac replied 7 months ago.
Thank you!On the left side edge of the board....there is a vertical black strip of connections.R,G,Y,W,C etc....can you post pic of that row of terminals please?Then we can get started
Customer: replied 7 months ago.
OK Billy here you go! I think you can see it from several angles.
Customer: replied 7 months ago.
Just to let you know I can run a separate set of wires from the control circuit to the NEST as they are only physically separated bye about 10 feet. The controller is directly above the furnace and their is a space to run wires. I would just as soon leave the old ones in place in case I need to go back.Marc
Expert:  BillyHvac replied 7 months ago.
Excellent pics, and I thank you.I see a black wire on R and one on G. This would appear there is a switch to run blower only...?Is this something that would remain? It would be redundant as the new thermostat should have a fan "on" switch. Tell me about those 2 black wires and we can get this done pretty easily.
Expert:  BillyHvac replied 7 months ago.
did you track the 2 black wires yet?

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