Alternatively, you can screenshot your wiring diagram before you disconnect the Nest from the wall. Open the Nest app, tap the Settings cog in the upper-right corner, then select Equipment > Wiring.

The wiring may also be switched for your fan settings. If you're comfortable doing so, you can try to switch the G wire, which controls the HVAC fan, with the Y wire, which often controls cooling.

2. Pop Off the Faceplate You’ll need to remove the faceplate of your old thermostat to get at the low-voltage wiring and backplate. It should pop right off with a little bit of effort.

Wiring adapter included: No; sold separately for $25 at Amazon, Best Buy, and Google. The fourth-generation Google Nest Learning Thermostat earns one of the top spots in our smart thermostat ratings.