Honeywell thermostat only R and C wires

[dcassett]

Hello, I've seen other posts on this subject and they seem to end up needing photos, so cutting to the chase. Existing thermostat is Honeywell, furnace is York, only 2 wires (R and C) at thermostat (others in cable exist but not used).

Adding: sorry, can't figure out how to post photos, but I do have photos of the thermostat back plate as well as the control board in the furnace, which I can post (if someone can help) or describe if necessary.

Further adding: posting links to photos. Back plate from existing Honeywell thermostat:

20241212_111245.jpg

Overall view of control board in furnace:

20241212_112435.jpg

Closer view of left edge of board:

20241212_112326.jpg

Closest view of terminals with best look at labels:

20241212_112348.jpg

I noticed that the jacket on the cable coming into the furnace control board (visible in the photos) is brown, whereas the one at the thermostat seems to be white or creme colored, which seems like it's a concern.

[GabrielaG]

Hi dcassett,

Thanks for reaching out to the community. I understand that you want to know how to connect your York furnace with two wires (R and C) with the Nest Thermostat. I will try my best to help you right now.

I've seen the photos you sent me of your control board and Honeywell backplate. The Nest thermostat requires at least two wires to function, one for power and one for heating or cooling. The wiring connection is shown in the picture, and there are additional wires on the control board that can be used with the thermostat; however, this needs to be checked by a Nest expert or your HVAC technician.

 Feel free to keep us posted if you have more questions.

Regards,

Gabriela