Atwood 8535 IV furnace

[Gary RV_Wizard]

Your challenge now is to figure out why is sooted up like that in the first place, cause it is gonna happen again if you don't. Caked soot like that is not normal, even after hundreds of hours of runtime. It only happens when combustion is incomplete. But  at least now you can stay warm while you think about it!

 

[Fatgnat]

The furnace has been running cleanly now for some time. The final fix, after cleaning it out and installing that relay to get the blower voltage up, was to reduce the manifold pressure. I was watching it smoke as I did it and as I lowered it the smoking stopped and it's been clean ever since. Apparently the manometer I got is inaccurate if that 11 inch spec is correct. It's down around ten now by that meter's reading. There's no more soot at the output and no more smell. That high pressure had it burning rich and incompletely.
I appreciate all your comments and suggestions!