Suburban propane furnace woes

[jovol]

Hey, I have a suburban SF-35 propane furnace in my 2011 Big Country. I’ve been having some sporadic issues with it turning on. A month ago it wouldn’t turn on unless I took the cover panel off and smacked it. So I took it out, cleaned out the intake and blower fan which had some dust but not a crazy amount, put it back together and it worked. Then a few weeks later it did it again. Took it apart again, maybe I shorted something on the control board, but I couldn’t get it to start at all on the workbench. So I ordered a replacement control board hoping that would fix all the problems. Installed the new board and it started up great. Reinstalled it, it worked for a few nights, now it’s doing the no start unless I smack it behavior again.

Could it be the motor, or something messed up in the fan that’s causing high starting resistance and when I smack it it loosens things up and gets going? Once it gets going it works fine, it’s just the getting started that’s the issue. When it fails to start, you hear one click like the relay switching, but nothing happens until you smack it.

At this point I might return the new control board and just get a whole new core until. Control board was about $110, a whole core is $400. But if anyone had some good insight, it might save me a good $300.

Thanks,
John

 

[jovol]

just learned that it could be the sail switch staying closed even when the blower stops. Then the sail switch doesn't open again until I smack it. Going to try replacing the sail switch.

 

[Dahillbilly]

the blower has to come on & run before the sail switch changes state from normally open to closed position & then the ignitor will click/spark. Blower has to come on 1st!!!

 

[Bogie]

Robert gave you the correct sequence. You should look at the Suburban Service and Training Manual in the Tools section of this forum.
You can find it here.
https://manuals.heartlandowners.org...CE_Service-and-Training-Manual-11-05-2015.pdf. It has a trouble shooting decision chart on page 30.

If the motor is not turning on by itself (after the click), but turning on when you "smack it". It may suggest that the motor may be failing.

 

[hoefler]

Replace the blower motor

 

[jovol]

Replaced the blower motor and all seems to be working well again. I don't think the original control board was the issue, but I must have shorted something out on it when I was testing things.

 

[wdk450]

The blower motor is a carbon brush type DC motor, and the carbon brushes typically wear out (actually grind down on the rotating commutator until they are too short to make reliable electrical contact).

 

[jovol]

Oddly the brushes look fine on the old motor, plenty of length. There was a bit of dust.

 

[Bogie]

Oddly the brushes look fine on the old motor, plenty of length. There was a bit of dust.

Though there is still plenty of length on the brushes, what you were experiencing a contact problem. Could be the brushes were not moving freely because of the carbon buildup. Or, the commutator was excessively dirty. If you feel energetic, you might want to clean up the old motor and test is several times after reassembly. Might be useful as a spare.

 

[Stormy61]

I'd agree on cleaning it up and seeing if it would work for a spare. But that black dust was def carbon wear-down from the brushes, so it may just have been those.