View Full Version : Armstrong SX 80 combustion fan motor

May 21st, 2004, 10:42 PM
This morning, a bird managed to get into the chimney, working his way into the combustion fan blades. The bird was wedged enough to stop the fan from turning. I took shut the power off, took the combustion fan out and removed what was left of the bird. I replaced the combustion fan back on the furnace and now I have more problems. Seems that as soon as I turned the breaker power back on for the furnace, the combustion fan motor runs for 5 seconds and then turns off for 2 seconds and then turns back on. This is cycle is constant, unless it calls for heat whic runs wells with no problems. It's only when the thermostat does not call for heat that the combustion fan runs and stops constantly. ( I have also change the chimney cap, it's bird proof now!) I hope you can help!!

May 21st, 2004, 10:58 PM
The combustion air blower is directly controlled by the ignition module (the "board" or "brain", as some refer to it). I have held the opinion for a while that these combustion air blowers and purge motors on furnaces should be separately fused, to isolate them from the rest of the system. A bird in the combustion blower is not all that unusual. A bird building a nest in there (during the summer) is also pretty typical. Bees have also been known to build their homes inside there over the summers. The trouble is, when the blower gets "jammed", it occasionally takes out some components on the board, since there is no fuse to blow to save the board's integrity. I'm about 90% sure that your control board is fouled up now. Sorry to break it to you. These boards can be salty. You have all summer now to save your pennies.

May 21st, 2004, 11:04 PM
Thanks for replying so fast! Is there a way to test the board? If I remove the power going to the combustion fan, I can hear the relay click as soon as there is main power to the furnace. (without the call for heat) Is there a way for me to "fix" this problem without going broke?

May 22nd, 2004, 09:58 AM
The only "fix" I can reccommend is a new board. If you read between these lines... I'd never reccommend that you put a little 24 volt relay in the line going to the combustion air blower that was pulled in on a call for heat. That would save buying a board, but I'm not reccommending that (if you get my meaning). That would invalidate the UL and AGI rating of the furnace.