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Thermostat doesn't have enough power for Wi-Fi

Community Member


I just installed a Nest Learning thermostat today and got frustrated that I couldn't find a definitive answer with respect to my 'blue' wire.  I went to the actual furnace controller (as suggested in the installation guide) and saw that the blue wire is labeled 'B/C' on the controller.  (There is no 'C' anywhere.).  Installation guide said to wire the blue into the "O/B" terminal on the NEST, but when I did that, the A/C unit would cycle on/off for about a minute and was 'clicking' when it was on.  After about 1.5 hours (+?) I looked at the thermostat and it was flashing a little red LED at the top and no display was possible.  Looked at NEST app on my iPhone and it said "Thermostat doesn't have enough power for Wi-Fi."  I know before I removed the old thermostat, the 'blue'/'red' combo gave me ~27VAC, so I'm *really* wondering if I should move the blue wire from the 'O/B' NEST terminal to the 'C' terminal.

I'm currently charging the unit with a USB charger and will plug it back in and check for power as suggested, but it would be AWESOME if someone could let me know if they think moving the 'blue' wire to the 'C' terminal is a good thing to try.

Any insight appreciated!!  

Thank  you!



Community Member

FWIW, here is a picture of the current NEST wiring and a picture of the furnace controller ...Current NEST wiringCurrent NEST wiringFurnace Controller WiringFurnace Controller Wiring

Community Member

NVM.  I moved the blue wire into the 'C' (NEST) terminal (after spending a LOT of time reading various threads and info in the guide) and clicking of the A/C stopped and the battery started charging and got above 3.8, after which the Wi-Fi connection was re-established and everything seems to be working. <fingers crossed>

Thought I'd post the 'answer' in case someone else was experiencing something similar.  FWIW, the furnace is an American Standard Freedom90 COMFORT-R.

Community Specialist
Community Specialist

Hi Rehauser,


I am pleased that you were able to resolve the issue. As we have a solution now, I will mark this thread as resolved and close it in 24 hours. Please feel free to open a new thread if you have any other questions or concerns.


Best regards,