Thermostat wiring connection

[DJGangel]

I am replacing an older Honeywell thermostat (not sure of model) with a Google Nest Thermostat. The old thermostat has only 3 wires colored red white, and green. They are labeled 1,2,and 3 respectively. Is the Google Nest Thermostat compatible with the older system and its wiring? If so, what is the appropriate label for the three wires?

if not, can they be made compatible?  

[aperezdeleon]

Hi DJGangel,

Thanks for reaching out to our community.

Determining if your system is compatible with a Nest thermostat can be confusing. Don't worry, I'm here to help.

All Nest thermostats use a standard wiring labeling configuration. This means that each of your wires is tied to a specific system function, like the G wire that activates the fans if you have a forced air system or the Y1 wire used to activate your system's A/C.

Since the wires in your system are labeled as 1, 2, and 3, they don't tell us much about what these wires accomplish. They could accomplish multiple tasks at the same time. That's why your system is not compatible with a Nest thermostat. However, there's still a chance your system might be compatible. You might need to contact one of our recommended technicians to determine if your system can be rewired to be controlled by a Nest thermostat.

Let me know how it goes.

Regards,
Angel.