C wire not detected

[BigKahunaFSU]

Hello,

I installed my nest thermostat. Everything seems to be working, but the C wire isn't being detected. When connecting through the home app it did flash that it wasn't detected, but i reset the wire and it went away.

How can I fix this, if I really need to since it seems to be functioning fine?

[CoolingWizard]

@BigKahunaFSU, if you removed the C wire from the backplate and reinserted it, and the C error went away then you solved the error condition. The Nest Learning Thermostat backplates have a 2-step contact for the wire.  The first step lets the Nest know the wire is present, the second is the electrical contact for the wire.  If it is not inserted far enough the Nest see the wire, but not the conductor.  if it was fully inserted and touching both contacts and then the C wire was disconnected at the other end you would get the same error.

AC Cooling Wizard

[BigKahunaFSU]

the banner that first said the c wire was undetected went away, but looking at the thermostat settings, it still shows c is not connected.  Even with it not showing that its connected, it appears that the AC is working just fine. I didn't know if I should be more concerned.

[CoolingWizard]

@BigKahunaFSU , sometimes the HVAC company that installed your system does not connect the C wire at the indoor air handler unit up to the C terminal. The only way to evaluate this as you will have to go to the indoor air handler. Remove the cover and look at the wiring and see if the color wire that you have on C at the thermostat is connected at the other end to the C terminal on the control board.   

AC Cooling Wizard