Nest says no power at c

[Nestdogg82]

My nest says no power at c..  tested voltage at thermostat base plate and shows 24v.  Reran wire, still 24vwith code 79.  Bought another nest thinking it was an issue with base... Still says no power.  Please help.

[CoolingWizard]

@Nestdogg82 When you used your multimeter did you use AC voltage setting? If you have 24Vac +/- 5 volts then you should indeed see it. make sure the wire, the bare copper, is straight and inserted fully.

AC Cooling Wizard

[Nestdogg82]

It was tested across rc/c and had 28 volts.  When testing from g/c I don't have voltage.  But it was explained to me c was more of a neutral in this situation.  I also get no power from my Goodman motherboard on c when testing to ground.  But I did use a jumper once from blue wire in furnace to a 24 volt transformer  to send an absolute 24 volt to c.  Still had error code e79.  Spoke with Google and they made it seem this has been an on going problem with these bases the thermostat uses.

[Robertobajo]

We are getting an E79 error message remotely. However, our AC guy was out and said unit was working fine and it’s likely a Neat app error. I reloaded app. Same error

[Robertobajo]

Is this C wire possibly loose? 

[Markjosephp]

Hi Robertobajo,

Thanks for posting on this thread. With this, it's possible, as your thermostat detects a wire in the C terminal but can't complete a circuit. You can also try removing the common wire and leaving it disconnected. Then, restart your thermostat to refresh it and see if the wiring report disappears. If so, check the power readings in the Technical Info settings and post them here.

Note: Turn off the power from your HVAC system at the breaker box before touching the wire.

Regards,

Mark

[Robertobajo]

Will the unit usually work (it appears to be) with this message? 

[Markjosephp]

Hello there, Robertobajo,

In most cases, the Nest Learning Thermostats can charge their built-in battery using your heating and cooling wires. But there are situations where you may need to connect the C wire to consistently deliver power to your thermostat.

With this, we can leave it disconnected, so you can still use both your heating and cooling. Leaving it connected may hinder your ability to control your system, as the display will only show the wiring report. In the long run, if you encounter any related issues said in this article, I'd suggest inspecting and fixing the C wire.

Thanks,

Mark

[CoolingWizard · Accepted solution]

If you understand Alternating Current, the R is the Line voltage and the Common is the neutral.  The Y, G, W and O are the power wires to activate the function. The thermostat connects R to Y for cooling, R to W for heating and R to G for Fan.  You should see 24Vac voltage between R and C or R and ground.  

AC Cooling Wizard

[Nestdogg82]

You are correct.  I do see voltages at the places you described above.  Still says no power to common on thermostat.  Would you agree with Google that the base is faulty?  If not, what would you recommend I try?

[CoolingWizard]

I would do one more thing first, Pull the C wire out, make sure the bare cooper wire is straight and long enough to reach the back of the connector.  

AC Cooling Wizard

[Jenelyn_O]

Hi there,

Thanks for posting in the Google Nest Community forum. Were you able to try the suggested steps provided by CoolingWizard? Please let us know how it goes.

I appreciate your help, @CoolingWizard.

Best,

Jenelyn

[Nestdogg82]

I tried what he suggested and it did not work.  I am assuming it is a bad base and trying to figure out how to send it back to Google for a free replacement.

[CoolingWizard]

@Nestdogg82 , You need to reinsert all wires, attach the display, then Goto SETUP > EQUIPMENT. It will show you a picture of the backplate and the wires that are detected.  Take a picture of that and upload it here.  After that continue until you can choose DONE.  Then Go to SETUP > TECHNICAL INFO > POWER,  take a picture of the power information. You and close pull up BASE information while in TECHNICAL INFO. Take a picture of that and upload it here.  Below are my pictures of this information I am seeking.

Equipment Detected DisplayBase InformationBattery and power information

AC Cooling Wizard

[Nestdogg82]

We are leaving town and packing, I do not have the time to do this but certainly will do it when we get back from vacation in a few days.  I am very familiar with this tech screen for power.  My c wire only shows 8 ma.  My voc and vin show practically nothing. 

[Markjosephp]

Hello everyone,

I wanted to stop by and see how I could help.

I appreciate your continued help here, @CoolingWizard.

@Nestdogg82, thanks for the update. Your common wire may not be properly grounded, so your system will report that it doesn't get enough energy. Could you please try removing the C wire again, but this time leave it disconnected? If you're getting the same wiring report, gather the power readings in the Technical Info. Then, move the power wire to the other power terminal to see if there are any changes.

Note: Turn off the power from your HVAC system at the breaker box before touching the wires.

Let me know how it goes.

Regards,
Mark

[Nestdogg82]

I am trying to upload the pictures you requested but can't seem to figure it out.  How do you upload a picture on here?

[Nestdogg82]

 

[Nestdogg82]

 

[Nestdogg82]

 

[Nestdogg82]

Doing this test I get 28 volts.

[CoolingWizard]

@Nestdogg82 , sometimes users do not fully insert the wire.  There are two sets of contacts, the first alerts the nest that wire is present. If you do not fully insert the wire, the primary contact might not be reached.  When it is the tab stays fully depressed.  If only partially inserted it comes back up slightly. 

AC Cooling Wizard

[Markjosephp]

Hey there,

Thanks for the continued help here, @CoolingWizard.

@Nestdogg82, I hope you've seen our response. I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having trouble from here, as I would be happy to take a closer look and assist you further.

Regards,

Mark

[Markjosephp]

Hi folks,

I don't want to be a nudge, but I'd like to check if you were able to get your thermostat working. Feel free to reach back if you still need help.

Best regards,

Mark

[Markjosephp]

Hello folks,

It has been a few days since your last replies, and we're going to lock the thread within 24 hours. If you have any questions, please feel free to create a new post.

Thanks,

Mark

[Nestdogg82]

Please do not lock the post.  I need help getting this fixed.

[Nestdogg82]

I have time tomorrow to troubleshoot the thermostat and I'm going to try everything everyone recommended and we'll get back with you shortly.

[CoolingWizard]

@Nestdogg82 , you need to use a Volt Ohm Meter and check the AC Voltage between the R and the C wires. If your meter reports about 24Vac, then your common wire is connected.  If however, your meter reports little to no power, you have to determine why.  

AC Cooling Wizard

[Nestdogg82]

I found the problem.  Someone spliced the wires under my house and only connected 4 wires and left my c wire snipped.  I am sorry for any inconveniences this has caused you, I reconnected wires and nest works now.  Thanks again, and sorry.

[Nestdogg82]

 

[Robertobajo]

I am the manager of Neat for my family. I invited my wife and she appears in the Google Home. But she can’t access the thermostat remotely. Any ideas?

[zoeuvre]

Hi all, 
 

@Nestdogg82, happy to hear that! I appreciate the gesture. 

@Robertobajo, it appears that your question is different from what was discussed in this thread. To avoid confusion, you can create your own thread where we can help you discuss your questions.
 

In the meantime, I'll go ahead and lock this thread within 24 hours. If you run into any more questions in the future, please feel free to create a new thread.
 

Thanks for your help, @CoolingWizard and Mark. 

Best,

Zoe