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FourIsWaltz 10-10-2010 05:58 PM

The Right Thermostat? (Honeywell says two diffrerent things)
I have a Rheem RGDA-100C-ER natural gas furnace, with a dual fuel kit (now running propane) and a CP-84R AC/heat pump. I'm in central Ohio, so it runs as a heat pump almost all winter with propane emergency/aux heat kicking in on a few cold days (and a/c in summer of course).

I tried to swap out the old thermostat for a Honeywell RTH7600, which is what Honeywell recommended.

The old thermostat has:
X, W2, R, G, O, Y, E, B.

The wiring diagram on the furnace control board has:
R, Y, B, O, W2, E, G, C (W2 and E are jumpered together).

The new thermostat:
Rc, R, O/B, Y, G, C, L, E, Aux.
The new one expects an L, and says I could run X to two places, but both already have wires in them (C that now has old B, and E). The instructions say panic!

Is there some way to use this thermostat, or is it going back to the store?

beenthere 10-10-2010 06:38 PM

B, on your old stat is the same as the O/B on the new one.

You don't need to use L.

FourIsWaltz 10-10-2010 08:19 PM

Thanks for the help, but I still don't quite understand. If I stick B into O/B, what do I do with O?

Wiring from the furnace to the new 'stat, trying to follow Honeywell's instructions:

'stat -- furnace
Rc -- nothing <-- (jumpered to R at the stat)
R -- R
O/B -- O <--(instructions say if there's an O wire, put B into C.)
Y -- Y
G -- G
C -- B <-- (but now what do I do with C?)
L -- nothing
E -- E
Aux -- W2

...and C from the furnace is just dangling there.

beenthere 10-10-2010 09:20 PM

Rheem uses B to energize the RV on a heat call. So your B from your outdoor unit should go on the O/B terminal.

You might want to write down what wires are connected where at your furnace and heat pump. And then post that info.

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