topic Re: Nest Thermostat 3rd G in Nest Thermostats

Nest Thermostat 3rd G

Moman2 — Sun, 22 Jun 2025 15:03:20 GMT

is my system compatible with Nest Thermostat. As you can see, there are 2 sets of wires. A set going to the left (labeled as W,RH,B,C). Another set going down (labeled as C,G,O,Y). By looking at the wires of both OLD and NEW system, I found out that the old system wiring has a seperate "O" and a seperate "B". While the new NEST system has only one wire called "OB". My question is which one from the old system goes to "OB"?

Re: Nest Thermostat 3rd G

Patrick_Caezza — Sun, 22 Jun 2025 04:44:12 GMT

@Moman2

Post a picture of the original thermostat's wiring here.

If the camera icon isn't present yet, you can use the Igmur.com Upload site and post the link it provides here.

Re: Nest Thermostat 3rd G

Moman2 — Sun, 22 Jun 2025 16:33:37 GMT

Thank you, Patrick. I was able to add the info you asked. Please check and let me know

Re: Nest Thermostat 3rd G

Patrick_Caezza — Mon, 23 Jun 2025 05:27:34 GMT

@Moman2

Can you post a picture clearly showing the thermostat's terminal blocks with labels showing? You have the RC terminal labeled as C.

If possible, can you take and post a picture of the terminal block on the control board in the air handler/furnace?

Re: Nest Thermostat 3rd G

Moman2 — Mon, 23 Jun 2025 17:55:40 GMT

@Patrick_Caezza, Here is another picture with labeled letters beside it

Re: Nest Thermostat 3rd G

Moman2 — Tue, 24 Jun 2025 13:44:26 GMT

@Patrick_Caezza, I replied to your question in the previous relpy. Can you check and let me know

Re: Nest Thermostat 3rd G

Moman2 — Tue, 24 Jun 2025 13:48:09 GMT

@Patrick_Caezza, As you can see, from the last picture I posted, one set of wires going to the left (labeled as W,RH,B,RC). Another set going down (labeled as C,G,O,Y). By looking at the wires of both OLD and NEW system, I found out that the old system wiring has a seperate "O" and a seperate "B". While the new NEST system has only one wire called "OB". My question is which one from the old system goes to "OB"?

Re: Nest Thermostat 3rd G

Patrick_Caezza — Thu, 26 Jun 2025 04:54:42 GMT

@Moman2

Apologies for taking so long. I got swamped with work.

The O and B terminals might mean it's not compatible with any Nest thermostat.

Take a look at the air handler and see where those two wires are connected.