I had a similar issue with a different wire on my thermostat. The best
thing I knew to do was open up the panel on the furnace and write down
the color of wire and the actual letter on the furnace board. The
previous thermostat wiring wasn’t 100% acc...
Give it a few days. I just installed mine this week and it was off about
+7 degrees compared to my previous thermostat sitting right beside it,
as well as another thermometer I had sitting close by. It has been 5
days and the Nest now shows the same ...