Have a friend with an old Rheem gas furnace and also central A/C... was
messing with it today because his air handler wasn't running on a
cooling call and therefore his A/C was all iced up and the house was
nice and warm. Thermostat checks out OK, currently the furnace has a
Honeywell S8910U ignition module and a Honeywell 47-22481-81 fan control
board. Neither of these appear to have been original to the furnace
which is a Rheem RGEB-06EC-FS which apparently originally came with a
Honeywell S-890G ignition module and I neglected to copy down the part
number of the original fan controller board (which was on the schematic
on the box cover) but I believe that the one that is in there is
actually the recommended service replacement.
Here's my question. I believe that the fault is in the fan controller
board; I am getting control voltage on "G" when the fan is manually
turned on at the thermostat and also when the thermostat is calling for
cooling but the fan does not run. I made a kludgy little harness to
force the fan to run 24/7 so he can have cooling. Rather than directly
replacing the fan controller, I found this online:
http://customer.honeywell.com/honeyw...px/ST9120U1011
Looks like a universal replacement for the same function, and has the
benefit of providing "HUM" and "EAC" terminals as well which is nice
(the old control does not have that, and he does have a humidifier which
I started to get working for him but never wired up because I meant to
bodge something together to interlock it properly and never got around
to it - the house did not really seem to need extra humidification even
over the winter. But it's there and the unit itself functions so he'd
like it to be working...) The description says "The ST9120U can replace
any ST9101, ST9120, ST9141 or ST9160 listed in Table 3 below" but I'll
be damned if I can find Table 3.
Could someone more HVAC literate than I tell me if I should recommend to
my friend that he order the part that I suggest above rather than the
direct replacement? It's $50-100 cheaper depending on source and will
make getting the humidifier working again a hell of a lot easier.
thanks,
Nate
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