I currently have a Trane Thermostat. I removed the cover, took a photo of the wiring diagram and went to the Nest compatibility chart. I have 2 legs of terminals - 7 wires on the left side and one on the right. The following is on the left terminals and a single BROWN wire on the right - see below.
Blue = O
Red = R
White = W1
Black = W2
Orange = O/B
Green = G
Yellow = Y1
RIGHT SIDE is Brown = BK
The BK is nowhere to be found on the compatibility chart. Any help is appreciate if the Nest 3rd generation is compatible.
BK wire is for dehumidification. Trane's thermostat will lower the fan speed by 30% when the temperature is getting closer to the set point, but the humidity level has not reached the humidity set point.
Nest won't support this feature, so cap it and push the wire into the wall.
@Prfssr, we wanted to follow up and see if you are still in need of any help. Please let us know if you are still having any concerns or questions from here, as we would be happy to take a closer look and assist you further.
I appreciate the help, Patrick_Caezza and Jenelyn.