![furnace - Connected C-Wire (previously unused) to thermostat, but still no power? - Home Improvement Stack Exchange furnace - Connected C-Wire (previously unused) to thermostat, but still no power? - Home Improvement Stack Exchange](https://i.stack.imgur.com/zx9IU.jpg)
furnace - Connected C-Wire (previously unused) to thermostat, but still no power? - Home Improvement Stack Exchange
![Wiring New Honeywell RTH6580WF Thermostat with no Yellow Wire at Thermostat - Home Improvement Stack Exchange Wiring New Honeywell RTH6580WF Thermostat with no Yellow Wire at Thermostat - Home Improvement Stack Exchange](https://i.stack.imgur.com/JTyJM.jpg)
Wiring New Honeywell RTH6580WF Thermostat with no Yellow Wire at Thermostat - Home Improvement Stack Exchange
![Substitute G-Wire for C-Wire -- Install the Honeywell Wi-Fi smart thermostat with this video. - YouTube Substitute G-Wire for C-Wire -- Install the Honeywell Wi-Fi smart thermostat with this video. - YouTube](https://i.ytimg.com/vi/p8Bb3e1mb48/hq720.jpg?sqp=-oaymwEhCK4FEIIDSFryq4qpAxMIARUAAAAAGAElAADIQj0AgKJD&rs=AOn4CLAA7USfkuQ7Noj7FQ0_lgLnqcwaTA)
Substitute G-Wire for C-Wire -- Install the Honeywell Wi-Fi smart thermostat with this video. - YouTube
![Old thermostat works, but I can't get the Honeywell T9 to work. T9 require C Wire that was not in the wall. I added C wire & RC wire via plug-in 120v Old thermostat works, but I can't get the Honeywell T9 to work. T9 require C Wire that was not in the wall. I added C wire & RC wire via plug-in 120v](https://i.redd.it/qgn9tccrp6a91.jpg)
Old thermostat works, but I can't get the Honeywell T9 to work. T9 require C Wire that was not in the wall. I added C wire & RC wire via plug-in 120v
![Does anyone know I can install a smart thermostat without additional wiring? How can I tell if the blue wire is the C wire? It's an air handler for a/c only. : Does anyone know I can install a smart thermostat without additional wiring? How can I tell if the blue wire is the C wire? It's an air handler for a/c only. :](https://preview.redd.it/x4o2gcbyfym91.jpg?width=640&crop=smart&auto=webp&s=31429b7c9e94f8a7ccdf5cba3a8bf9bc94e7629e)