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frustrating nest thermostat

haz
Community Member

Where to begin? Just received a free Nest thermostat from my power company (SRP).  Removed the Honeywell (4 wire heat pump system) and logically mapped the wires to the Nest (semi-verified with the confusing available internet info).  Trouble with internet connection to Nest, so decided to first just test the hardware, i.e. use it manually.  Manual operation very non-intuitive but eventually see it delivers heat instead of cold.  Further attempts to debug stopped, as before I can test alternate temp or wiring settings I can only get an error message (for developers no less!) n292.   

Any thoughts?  I'm not hiring a pro.  I'd really like to see it can run manually before working on the web connection...otherwise it's going back!

1 ACCEPTED SOLUTION

haz
Community Member

Finally a solution.  I report it here in case it helps others.  My Trane system had a blue wire connected at the air handler but not at the thermostat.  We dug the blue wire out of the multi-conductor wire and attached it to the Nest. 

The system worked better but still some problems and worse, I could measure 26V blue:red at the air handler but 15V at the thermostat.  This doesn't make sense.

Finally the solution:  there are two multiconductor wires spliced in at the air handler.  They both disappear into the ceiling but presumably one goes to the thermostat and the other to the compressor outside.  (I hadn't paid much attention to this.) A close look at the splices showed 3-wire connections for green and yellow but only two for blue.  We dug out a blue wire from  the (now clearly) disconnected multiconductor wire and added it the splice.  Now 26V at the thermostat and Nest works fine.

View solution in original post

9 REPLIES 9

haz
Community Member

An update:  I got rid of several errors and got normal working via the Android app by paying attention to this thread https://www.doityourself.com/stry/hot-topics-nest-thermostat-c-wire, which seems to address a system like mine.  Net: put the green wire (connected to G on my Honeywell) to C on the Nest.    Still getting heat rather than cool though.   

Patrick_Caezza
Gold Product Expert
Gold Product Expert

You do not want to use the G wire as a C wire trick, it will drive you nuts as you lose control of the fan.

Post a picture of your original thermostat's wiring and I'll offer a suggestion.

The Nest Thermostat requires the Nest Power Connector or a common ("C") wire. Based on your system and wiring setup or your use of a zone controller, you’ll need the Nest Power Connector or a C wire to use this thermostat. Be sure to add a Nest Power Connector to your cart. See g.co/nest/cwire for details.

haz
Community Member

how do I post a picture?

Ryan_G
Community Specialist
Community Specialist

Hi haz,

 

Thanks for being here in the community.

 

You can click the camera icon on the top part of the reply page and then browse and upload the photo you want to share.

 

We're looking forward for your reply.

 

Best regards,

Ryan

haz
Community Member

Thanks, I'll try though I had problems before.  Check the link I embedded above for a semi-lengthy discussion trying to debug my problem.  Cliff note version:  our air-handler has a (previously unused) C wire which I've connected and moved green back to G.  It almost works:  controls temp as expected but shows error (N262) on Nest display, so I'm still not happy.  Voltage at Nest is weird (14V B:R) but 26V at air handler.  Not resolved yet...

 

(Sorry I find the menu that pops up when I click camera icon is not clear enough for me to insert a pic)

Ryan_G
Community Specialist
Community Specialist

Hi haz,

 

Thanks for your reply. 

 

Let's try doing a complete factory data reset and run the setup process again with the C (common wire) connected this time already.

 

Let me know how it goes by replying to this thread.

 

Best regards,

Ryan

haz
Community Member

Finally a solution.  I report it here in case it helps others.  My Trane system had a blue wire connected at the air handler but not at the thermostat.  We dug the blue wire out of the multi-conductor wire and attached it to the Nest. 

The system worked better but still some problems and worse, I could measure 26V blue:red at the air handler but 15V at the thermostat.  This doesn't make sense.

Finally the solution:  there are two multiconductor wires spliced in at the air handler.  They both disappear into the ceiling but presumably one goes to the thermostat and the other to the compressor outside.  (I hadn't paid much attention to this.) A close look at the splices showed 3-wire connections for green and yellow but only two for blue.  We dug out a blue wire from  the (now clearly) disconnected multiconductor wire and added it the splice.  Now 26V at the thermostat and Nest works fine.

MelbaDT
Community Specialist
Community Specialist

Hey Haz, 

 

Appreciate your time for sharing the detailed solution you've found. This will be a great help to anyone out there who might be experiencing the same concern in the future. Give yourself a pat on the back for a job well done!

 

Cheers, 

Melba

MelbaDT
Community Specialist
Community Specialist

Hi, 

 

I haven't heard from you in a while so I'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