nest thermostat connections

[wjulaxer13]

i am looking at my current thermostat wires to determine if they are compatible with my new nest thermostat. The original thermostat has connections for R, W, G, Y, and W2. No C wire. The nest connection choices are R, W, G, Y, C, and O/B. No W2 connection. If I understand correctly, the W2 is an auxilliary connection and the O/B connection is for a heat pump. Does this mean that I can connect the W2 somewhere like the O/B connection (which doesnt make sense), do I need it at all, or does this require me to add a C connection. It is not at all clear to me. Any help will be appreciated. Thank you 

[wjulaxer13]

as i look at my wiring the original thermostat I noticed that all the wires match the colors that are associated with their designation in the charts. The W2 wire is blue which I would guess would mean it is the B wire. Does this help me to determine it goes into the O/B connector? 

[Hug3kids]

Which thermostat do you have ?  I believe both Y2 and W2 are for 2 stage cooling and 2 stage heating.

I think only the learning thermostats support 2 stage.  I have a 3rd gen learning that has these.  You may still need a "C" wire.

[wjulaxer13]

The thermostat i am replacing is a Lennox X4147. I have attached the photos of the current thermostat and the new thermostat. Thank you.

John

  

[Hug3kids]

What kind of heat do you have ?  It looks like you have a 2 stage heat system from looking at the wiring on your old Lenox thermostat.  You may need to check with Nest support to see if there is a way to make it work, but think you may need the more expense thermostat to replace this one.

[wjulaxer13]

I think what confuses me is that my current thermostat is also a 'smart' thermostat and as such must have a common wire to provide constant power. The only wire I see that could work would be the blue wire connected to the Aux port. Blue is used in common port wiring as well but i didnt think using the aux port would provide continuous current to the thermostat. 

[Hug3kids]

probably not.  Do you know what the aux port was connected to on your old thermostat ?  Do you have a humidfier, zone damper or other device that it could be controlling ?

[wjulaxer13]

I hadn't thought of that but there is a humidifier on the furnace. Good catch. I was under the impression that smart thermostats used a common wire for its continuous current. Apparently not.

[Jake]

Hey all,

Sorry for the late reply. I wanted to follow up and ensure you are good to go. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further. 

Best regards,
Jake

[Jake]

Hey all,

I want to ensure you are good to go, and everything is working properly. Please let me know if you are still having trouble, as I will be locking the thread in 24 hours due to inactivity. 

Best regards,
Jake

[Jake]

Hey all,

It has been a few days since the last reply, and I am going to lock the thread at this time. If you have any questions, please feel free to create a new post. 

Best regards,
Jake