Need help with identifying wires on Honeywell TH9320WF5003, using Nest compatibility checker to replace with Nest gen 3

One of wires look like "W- O/B, not sure which wire it really is nest doesn't have this wire option?

On Honeywell I have wires going into C, RC, R, W- O/B, Y, G

Home has 5 zones baseboard heating and 2 zones a/c, replacing one of thermostats that controls both a/c and heat

picture of thermostat connectors, top right connector has me confused, looks like "W- O/B" enter image description here

  • 1
    Can you post photos of the wiring at both ends? Commented Aug 11, 2018 at 15:13
  • We need to see the wiring at the furnace/air-handler end as well Commented Aug 12, 2018 at 21:01

1 Answer 1


As per https://www.doityourself.com/forum/thermostatic-controls/596703-honeywell-nest-thermostat-wiring-help.html

I used following wire mapping from honeywell to nest and I have been up and running for a few days without issue

C = C

Rc = Rc

Y = Y1

G = G

R = Rh

W = W1

  • 1
    In case it's of any use: C = Common wire (used for electrical COM for thermostats requiring a 24VAC power source), Rc = +24V for cooling circuit (often bridged with Rh), Rh = +24V for heating circuit, Y# = Cooling (# indicates the zone, if more than one), W# = Heating, G = Fan
    – Shamtam
    Commented Aug 15, 2018 at 2:33

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