I don't believe it's a wiring issue. Try these instructions from
https://support.google.com/googlenest/answer/9257086, 3. Change the O/B
wire settings:Open the Home app .Tap your thermostat.At the top right,
tap Settings.Select Thermostat.Scroll unti...
Please attach a picture of the wires connected to your Nest Thermostat.
If you took one of the wires on the old thermostat, include it as well,
otherwise a picture of them attached to the air handler would be
beneficial.
The O wire on your current thermostat goes into O/B on the Nest. Trane
likes to label the common wire as B, so that one would go into C on the
Nest. If you want to be sure, check the wiring on the air handler side
and if I'm right it'll be labeled "B...
