Nest 4th generation wiring question

[skbem35]

Hello,

I am looking for wiring help for my 4th gen Learning Nest.

Existing system:

My system is a two-zone system, with both zones being the 2000 era mercury dial thermostats.  I do not have a heat pump.  The system is forced hot air, and cooling.  The master thermostat location controls the second zone.  in other words, the second zone thermostat function if the master thermostat is toggled off.   The master thermostat switch needs to be in the heat or cool mode for the second zone thermostat to work.

the current wiring at the master thermostat location is as follows:

blue wire to "B" screw

yellow wire to "Y" screw

brown wire to the "O" screw

red wire to the "R" screw

green wire to the "W" screw

I have installed the learning Nest at the Master thermostat location.  The nest will operate the primary zone, but the secondary zone will not work.   I contacted Google Help 3 times, and got two different wiring options (neither of which worked to provide power to the second zone).  The third Google Help tech told me to contact Ontech Pro.   

Ontech Pro costs $150 so i wanted to try out this forum first.

The first tech told me to wire the B wire to the C, and the O wire to the OB, then all the others the same (R, W, Y etc).

The second tech told me to only use the R, W and Y wires, and do not use the B or O wires.

Both these wiring scenarios led to the same result: the primary zone functions correctly with the Nest operation, but the old secondary thermostat does nothing now.

any advise would be greatly appreciated.

Thanks,

Scott

[Jeremyg]

Hi @skbem35!

Thanks for reaching out to the community. I understand that you want to start to use the Nest Learning Thermostat 4th generation, but no need to worry; help is here. We appreciate all of your previous troubleshooting efforts. In this situation, could you please share a picture or the wiring that is going to be helpful to better understand the compatibility of your system?

I'll be waiting for your response; any additional details you can provide will be helpful.

Best regards,
Jeremy.

[skbem35]

Hi Jeremy,

thanks for responding.

I am not seeing any way to upload a picture?

Thanks,

Scott

[Jeremyg]

Hi @skbem35!

Thank you for your reply. I appreciate the steps that you have taken with your thermostat. I understand that you want to connect the two zones for your HVAC system. I am happy to continue assisting you.

Based on the information you provided to me, I see that you have five wires connected to your previous thermostat, and I guess it is the way that you connected this Nest thermostat as the information you gave me. My recommendation is to connect the B to C, and the O wire does not need to be connected if you do not have a heat pump. Also, to connect the second zone, you can refer to this article: Zoned system compatibility with Nest thermostats.

Please keep me posted.

Best regards,
Jeremy.