Can I connect Nest 3g thermostat to my heat pump system?

[JW54]

I have a blue wire labeled 'T2' but Nest does not have an option for this wire.  Says my wiring is incompatible.  What is this wire for?  Is there any way to connect this thermostat?

[JW54]

Google results indicate the T2 wire may be for a second thermostat.  I don't have a second thermostat that I know of.

[SoriaD_]

Hello @JW54  

Thanks for reaching out to our Nest Community about this wiring configuration. I apologize for all the inconvenience. Don't worry; I'm here to help you with it.

I appreciated the details you provided us; all that information is very useful in finding a solution for you. To understand your system a little better, let me ask you if you have a picture of the wiring of your previous thermostat. This is to determine if this wire is compatible with our Nest thermostat.

Please keep us posted; I'm happy to assist you.

Best regards,

Douglas.

[JW54]

Not sure how to upload photos... Here is my 1st attempt 

[JW54]

https://photos.app.goo.gl/mAzDJEvb8Nz9x4hK9

Looking at this photo, Y2 is more accurate than T2 since it is a heat pump

[SoriaD_]

Hello @JW54 

Thanks for your reply. I appreciate the information you provided me. Let's take a look at the answer. 

According to the details, I can see we have no problems connecting the wiring configuration to our Nest Thermostat. Here is an example with the Nest learning thermostat:

If your interesting to change your actual thermostat you can find this Nest thermostat on this page: Nest Learning Thermostat.

Feel free to keep posting if you have more questions. I'm happy to find a solution for you.

Best regards,

Douglas.
 

[JW54]

The issue is for the blue wire, I was looking at the wrong label for non heat pump T2.  Once I realized it was Y2 then I had no issue with the installation.  Thanks

[JW54]

Now the setup software is warning me that I must choose the proper settings or I could ruin my heat pump  AC unit.  I don't know what settings to select.  At this point, I'm not even sure I have a heat pump.  My outdoor unit is a lennox xc21-048-239-02.  While this unit is very efficient, I cannot confirm this is indeed a heat pump, let alone if it needs to cycle seasonally or every time.  Any hints?  FYI, there is gas to the inside unit, but that could be a backup heat source for frigid temps.

[JW54]

I already purchased the learning thermostat.  I installed it, and guessed on the setup and tested it.  For the heat tests, it only blew cool air.  I didn't try the heat tests, but when I exited testing, the thermostat called for ac, but the heat came on, so I swapped back to the old thermostat.  Looking at the diagram you provided, all the wires were the same except the app had me connect the red wire to Rh.  This did not seem correct since my original setup was R and RC with a jumper.  That must be why heating and cooling were reversed.  I'll try again tomorrow.

[JW54]

 i restarted installation on the nest app and this time selected R and Rc, but the app still instructs me to use Rh.  Also, to the question asking if I have a heat pump, I answered 'don't know ' and based on my o/b wire being white, it advised me to continue with standard labels (not heat pump).

[JW54]

I installed the thermostat again using your suggested wiring diagram, switching from Rh to Rc.  For whatever reason, heating and cooling are still reversed.  I read online that when this happens, switching the O wire setting to B will fix this, and it did.  It is now cooling fine.  Can't test heating since it is so hot in Texas right now.