York T874r1046 Thermostat Wire Color Codes

[itchibahn]

I have two York F2RP036H06B units, one upstairs and one downstairs, with an old York T874r1046 Thermostats. Both thermostats have 6 wires used: W, B, G, R, Y, and O. I'm trying to replace the old thermostats with new Hunter 44272 thermostats. I got AC to work but heat is blowing room temperature air.

Original wiring was as follow:
Wall York
------------------
Red R
Yellow Y
Green G
Orange O
White W
Black B

I think:
R - 24v ac power heating
Y - compressor contactor
G - fan relay
W - heat relay
B - 24v ac common

But not sure what O is.

I've connected to Hunter as shown on manual:
York Hunter
----------------------
R R (Rh/Rc)
Y Y
G G
O O
W A/E
B C

Please help. Thanks.

[al]

O used to be the connection for the 4 way valve, you may need to trace the outdoor unit wiring to confirm, you may get away with looping o and w so valve energises with call for heat.

al