New Nest Learning Thermostat not getting power from C wire

[adamc909]

• Need help with my nest thermostat. Just installed it and it said no power coming from C wire. I disconnected the C wire and the error message went away but the thermostat isn’t charging. 

[CoolingWizard]

@adamc909 , sometimes the installer did not connect the wire bring attached to C at the thermostat to the C terminal in the HVAC air handler.  The Nest Learning Thermostat 3rd generation can detect a wire that is inserted. So it detects the wire as present but the terminal contact is further in so the wire must be stripped to the proper length and then fully inserted. 
Do you feel confident in your skills to open your HVAC air handler?

AC Cooling Wizard

[adamc909]

Yeah I do feel confident to do that, but I also used my multimeter to test the c wire with the Y wire and found it had 26.5V, so the power is there. I pushed the c wire as far back as it could go while depressing the tab (even more so than the other wires that are definitely showing up with no error code on the thermostat. 

[CoolingWizard]

@adamc909 , when testing the C wire with a Volt Ohm Meter, always test C to R for the test. You should not get a power reading on C to Y at the thermostat end. And, the only way to get a voltage on C to Y os at the HVAC air handler and when the Nest Thermostat is calling for Cooling. 

AC Cooling Wizard

[juliawhites]

Check if the C wire is properly connected and ensure it’s securely attached at both the thermostat and the HVAC system. If the issue persists, consider using a different C wire or installing a C-wire adapter.

[adamc909]

I’ll check the connection at the hvac.
Aren’t c wire adapters for hvac systems that are missing the c wire? 

[CoolingWizard]

@adamc909 , if there is a wire, not being used at the end, where the thermostat is, that can be repurposed and used as a common wire for the power. If however, you don’t have any more available conductor wires to reuse, then yes to get to see signal on your system to the nest might require the nest power adapter. whenever possible, always use a conductor wire if one’s available. 

AC Cooling Wizard

[jelisjack4]

It is like the C wire might not be connected properly or there could be an issue with the power source. Make sure the C wire is securely connected at both the thermostat and the HVAC system. If the issue persists, you might want to check the transformer or consult with a professional or business 2 for ensure everything is set up correctly.

[CoolingWizard]

@jelisjack4 , to check an HVAC control transformer, you only need a Volt Ohm multimeter.  At the HVAC indoor air handler, Check the AC Voltage between R terminal and the C terminal.  

AC Cooling Wizard