Old thermostat has an unused blue wire, should i use it for nest 3rd What all those letters mean on your thermostat’s wiring Thermostat wiring diagram mean letters wire 2wire only where ifixit thermostats which goes
What All Those Letters Mean on Your Thermostat’s Wiring - iFixit
Thermostat unused wires
Old thermostat has an unused blue wire, should I use it for Nest 3rd
What All Those Letters Mean on Your Thermostat’s Wiring - iFixit