C wire not getting power...but it powers my current thermostat!

[bill1724]

My current tstat works fine and is powered by a C wire.  When I install the Nest, it tells me there is no power from the C Wire.  I've checked all connections multiple times.  I've spent time with tech support, and the best they can tell me is there is no power to the C wire or it isn't grounded properly.  Since my current tstat works (and doesn't have batteries, so it is clearly getting power from the C Wire), I don't really want to spend $160 on one of the Nest pros only to have them come out and tell me either the Nest isn't compatible (which the tech support person told me it is) or it is defective. 

Does anyone have any other suggestions for what could be causing the Nest to not be getting power from the C wire?  The tech also told me it would have nothing to do with the Nest batteries (I was thinking maybe the batteries are too low...but they said that's not the issue).

Photo of current tstat wiring attached.

[HVAC]

It might be connected at the thermostat but not ant  air handler/furnace circuit board. Need to check it there & maybe take a pic of it if possible. Your existing stat was probably getting power for the red wire. The C slot refers to common or neutral the R slot is the wire that provides voltage. need to verify 24 volts between R & C. Good luck 

[bill1724]

Thanks for the feedback.  From what I can tell, the C wire is connected at the main board.  Any other thoughts?

[HVAC]

You’re correct Seems like it is. There’s a black wire also that’s wire nutted with the blue wire to C and a white wire wire nutted to yellow going to the Y on the board. Where does the black and white wire lead to? Maybe a condensation pump that’s unplugged? Or safety auxiliary switch that’s acting up causing power loss. 

[zoeuvre]

Hi folks, 

@bill1724, thanks for reaching out to us, and I'm sorry to hear about the situation. I want to check and see if you are still in need of any help. If so, please answer the following:

1. What type of Nest Thermostat do you have?
2. Who installed the thermostat?
3. What is the exact message or code that appears on the thermostat or on the app?
4. What is the power reading of your thermostat under Settings > Technical Info > Power (Battery, VOC, VIN, and lIN) if you have the Nest Learning Thermostat or the Nest Thermostat E and Settings > Equipment > Power Info (VIN, IIN, PS-*) if you have the Nest Thermostat 2020. 

Please send us a photo of how are the thermostat wires connected to your Nest Thermostat's base. Also, if you have a voltmeter, use it to check the voltage that the C wire has.

1. Set the dial to 200 VAC.
   • If the multimeter doesn’t have a 200 setting, choose 100 or 250 VAC.
   • The general rule of thumb is don’t set it too high (500+) or too low (50).Place the red lead on the R wire.
2. Place the black lead on the other wire being tested (W1, Y1 or C).
3. The normal readout should be somewhere between 20 and 30 V (24 V is most common).

Let me know how it goes. I'll look forward to your response. 

I appreciate your help, @HVAC. 

Best,

Zoe 

[bill1724]

Thanks for the note, but I gave up on the Nest and went with Amazon's smart thermostat, which is functioning properly.

[zoeuvre]

Hi bill1724, 

We're sad to see you go. We're always here to help if you ever change your mind. If you have questions or concerns in the future, feel free to start a new thread, and we'll be happy to help.

All the best,

Zoe