Wiring guide
Google Nest Learning Thermostat (4th gen) wiring for 4 wires, no C wire
Good news: the Google Nest Learning Thermostat (4th gen) is a direct swap for this setup. Every wire has a matching terminal.
R, W, Y and G is the classic furnace + central AC setup found in millions of US homes, one wire short of what most smart thermostats want. The fix is usually an adapter at the furnace, not new wire. Read the full 4 wires, no C wire guide for how to confirm your setup and mistakes to avoid.
Wiring diagram
Google Nest Learning Thermostat (4th gen)
Works: direct swap| Wire | Color | Job | Connect to | Note |
|---|---|---|---|---|
| R | red | 24 V power | Rc or Rh | |
| W | white | Heat, stage 1 | W | |
| Y | yellow | Cooling, stage 1 | Y | |
| G | green | Fan | G |
Install steps
- Turn off power to the furnace/air handler (switch or breaker) and the AC condenser. Confirm the old thermostat is dead.
- Photograph the old wiring, then label each wire with the letter it came off. Ignore short jumpers.
- Connect each wire to the Nest Learning (4th gen) terminal shown above. Cap unused wires one at a time.
- Restore power and finish setup in the app using the settings below.
- Test heat, cool and fan. If a breaker trips or equipment runs nonstop, power off and call a pro.
App settings to choose
- Single R wire: the Nest app tells you whether to use Rc or Rh.
What you need
- Google Nest Learning Thermostat (4th gen)The thermostat itselfCheck price
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Confirm against the official Google Nest install guide. The app also checks your wiring during setup.
Frequently asked questions
Where does each wire go on the Nest Learning (4th gen)?
R → Rc or Rh; W → W; Y → Y; G → G.
Do I need a C wire for the Nest Learning (4th gen)?
No C wire: Nest usually runs on power sharing. If it loses Wi-Fi or its battery drains, add the Nest Power Connector.