Just wanna add that you might consider taking a multimeter and checking for 24 volts between the R and C terminals to confirm the blue wire is, in fact, a common wire. If not, then installing the Nest power adapter as you initially planned would be the right way to go. But if you're not 100% confident or run into other issues, sometimes it's best to bring in the pros. Companies that specialize in AC repair like ac repair in Riverview, FL are well-versed in HVAC systems and smart thermostat installations. They can provide expert services that go beyond just a quick fix, ensuring that everything is set up properly and functioning efficiently.