Wiring a Nest thermostat with a O and B cable?

[chuckbag]

I have a York Diamond 80 furnace/AC/heat pump unit with a Ultra-Zone Model EWC-ST-2E Control Panel.  

The control panel connects to the thermostat, and provides the following labeled outputs, and I figured to plug them into the nest's inputs as such.  My challenge is understanding where I plug the "O" and "B" cables into.

Control Panel Output	Nest Input
W (heat)	W1
Y (cool)	Y1
RH	RH
O	?
B (fan on)	?
G (fan auto)	G

I've read some places to put the O in the OB jack, and the B in the C jack, and in others the other way around, and others to use the [*] jack instead.  

Any thoughts on how this should be wired in? 

[David_K]

Sometimes both the O and B wires are connected at the thermostat but the wires are not actually attached to anything at the other end on the system control board, so it's worth checking that.

Strictly speaking Nest Thermostats are not directly compatible with systems that need both O and B wires. Those wires control when your heat pump cools or heats your home. It is possible to add a relay to resolve this, usually at a zone control panel, in order to make it compatible but for that, I'd recommend consulting professional help. I'll link below guidance on how to do that.

Get installation help or HVAC service from a professional - Google Nest Help