Power Test Not Run on Nest Thermostat

[mormegil27]

I installed my Nest (Thermostat-1.4) w/ C-wire, only to discover the C-wire was not connected.  So I opened my furnace and sure enough the C-wire was disconnected (who knows why, given that someone went through the bother of running it).  Ok, easy, I connected the C-wire to the furnace C-terminal and reconnected the Nest.  Went through the app instructions to add the C-wire, and the C-wire shows as being present.  

Ok - but if I go to: Equipment -> Power Connector -> Power Status

... it has what looks like an error, with "Power Test Not Run" and "g.co/nest/m25".  Well ok, so I ran a Power Test, and nothing happens.  Still shows the same thing.  I go to that link, and it says absolutely nothing about "Power Test Not Run".  

I don't know what's up with this.  My main question is how do I know my C-wire is actually powering the Nest?  If I go to Power Info I get: 

lin: 385

PS: C-385

I assume this just tells you some kind of C-wire standard.  

Can anyone help me perform the power test?  Yes, I know how to do it in the menu, but it doesn't actually appear to perform the test.

[mormegil27]

Ok - after contacting Google support it appears that there is a grounding problem with my c-wire on my HVAC side.  The Nest appeared to go to "Very Low Battery" overnight (in less than 24 hours), but after disconnecting the c-wire the battery returned to a normal reading (i.e. < 1500 mOhm). 

So if you encounter this problem, you most likely have an issue with your c-wire not providing the proper voltage (or not being grounded properly).  

Further, the Nest literature states that the Nest can sometimes get all it's power from the RYWG wires without a C-wire, but I suspect based on my conversation with the help desk that not having the C-wire will still slowly discharge the battery.  

With the c-wire disconnected, the Power Status does now say "Not Detected".  

What's interesting here is that just having a c-wire on your HVAC will not guarantee you can use a Nest without battery replacement.  In my case, my configuration has some unusual c-wire setup that makes it incompatible.

[MelbaDT]

Hey mormegil27, 

Thanks for posting and for keeping the thread updated on what you've done to isolate the cause of the issue. Have you had the chance to have your C wire checked by a local HVAC technician?

Best, 

Melba

[MelbaDT]

Hey there, 

Checking back in should you still have some questions here. Let us know by replying to this thread. 

Best, 

Melba

[MelbaDT]

Hi, 

We haven't heard from you in a while so we'll be locking this thread if there is no update within the day. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the Community.

Best, 

Melba