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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22542
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Airheatman I have a Trane XL80 furnace along with central AC

Customer Question

Hello Airheatman
I have a Trane XL80 furnace along with central AC unit. I have a White Rodgers thermostat model 1F81-261.
Currently, I have a 5-wire bundle and all are connected at the furnace end and the thermostat end. I understand this thermostat can be hard-wired for power using its C terminal. I would very much like to hook this up, as replacing batteries a few times a year seems silly (and reprogramming is even more so each time).
The C terminal in the thermostat is not connected at this time.
The connections from FURNACE > THERMOSTAT are as follows:
W2 > W2
W1 > W
R > R
G > G
Y > Y
In addition, there is a 2 wire bundle going from the furnace out to the compressor. This bundle has :
- a green wire connected to the "B/C" terminal at the furnace,
- a white wire connected to the "Y" terminal. This Y terminal also has the yellow wire going up to the thermostat.
I would like to get a wire up to that C terminal at the thermostat to give it power. Based on this configuration, am I able to connect an 18 gauge wire from C terminal down to the furnace control board... and to which terminal should it be connected to?
I have images to back all this up... if it helps, but not sure how I can get them to you.
Thanks very much for guidance!
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.


My name is Billy.

The terminal in furnace labeled B/ has a green wire from outdoor ac unit...this is
"common". You will add a wire from that terminal, at other end to thermostat C. Make sure power is off to furnace when doing this. You can have more than one wire on B/C

And 18g is great