I have on old White-Rodgers 4 wire single transformer system I believe. Model 1F76W357.

I am installing a Honeywell RTH3100C non programmable thermostat.

Wires on the White-Rodgers are:

RC RH (Jumpered inside the thermostat)
W
Y
G

Wires on the Honneywell are:

E
AUX
Y
G
O
L
R
B
C

I tried to hook it up like this:

RC/RH = R on the Honeywell (RC and RH are 1 wire out of wall)
W = AUX on the Honeywell
Y = Y on the Honeywell
G = G on the Honeywell

When I turned the heater, after 3 minuts the AC Kicked on.

Online, I have learned that on the old White Rogers these wire are:

Y=Cooling System
G=Fan Relay
W=Heating System
RC/RH=24v Hot

So I tried a couple of other combos and no luck, I just can't figure out the whole RC/RH thing.

Please let me know if there is an expect that can help.

KMC

Sounds like what you have is a thermostat that is intended or configured for a heat pump system. May need to get one that is right for the type of system you have.