4th gen google neest compatibility check

[Jimmy67]

My old system has three wire. The connections to the old Honeywell system are labelled R, O/B, and G.

[CoolingWizard]

@Jimmy67 ,

You need to look at the opposite label the OB wire is attached to.  You should have a wire on W or Y. In all likelihood yours is a gas furnace so it should be W. 

The Cooling Wizard

[Jimmy67]

Thank you CoolingWizard- yes, its a gas furnace, and the other end of the wire it says W.

[CoolingWizard]

@Jimmy67 ,

So your old thermostat has both a heat-pump markings and conventional markings.  The other side of the OB is likely marked W or W1.  

The Cooling Wizarx