Google Nest Community

With that thermostat the blue B wire would be a C for Nest.The black W2/X2 would be an E wire in most cases - used for emergency heat. Best to find the wire at your air handler and see what it is connected to. Most times it goes to the same place as ...

Tape off the brown E/W1 wire and any will work. If you want separate emergency heat control then you need the 3rd Gen Learning version.