Hi all.. In my search for furnace issues I am experiencing I came across you thread..
I do not own a keystone but a coachmen with a suburban furnace.
Ive read this post carefully and you all should stay on track to the issue at hand.
With thats said my issue is the same as the op's and may have more theroys on whats going on.
My background is I am a plumber 35 years.
So I have a 2018 coachmen with a suburban furnace. The first thing I noticed with the furnace and the manufacturers build on this SF 30 was they only installed 3 ducts. This is a 26 ft camper.
After turning on the furnace I notices it goes off on high limit.
Suburban states 3 ducts minimum for the SF 30. Thats fine I have 3 ducts but one is right next to the furnace going through the wall to the master. The other two are 20 ft away at the buck area and rear bath.
So why did I think the cause of the high limit is cause by? Lack of air flow I think.
So calling the dealer they sent me a whole duct kit. I installed this close to the furnace under the couch. ( Just a note all the 2017 units had this 4th duct because the furnaces of that years were an SF 35. That furnace requires 4 ducts)
so when the furnace goes on and off on high limit it will take a long time to heat the coach for sure.
Thats what I think the OP is experiencing. His may be a simple limit switch replacement for 6 bucks.
On the other hand my furnace it definitely overheating. The temp out of the ducts is extremely hot. But because of this high limit switch turning the burner on and off every few minutes I dont think the coach will heat properly in cold temps.
So for now I added a 4th duct. I have room in the plenum for a 5th which I may also add.
But here is a wrench ill throw in. Im testing my furnace when its 85 f out. Is it possible the incoming air into the unit is too hot and this is normal operation? ( I know you guys are testing in cold weather) I may have to wait till cold weather hits to test my theory to see if furnace limit switch kicks off the burner.
IMO the burner should not kick off by the limit switch.
I have not figures out my next course of action, but my dealer also is 4 hours away. And I aint driving that far for anything period. I will fix myself if need be..
But the good tip I got from here is the warranty on the furnace. I have a suburban auth center a few miles from my home.
I am going to go there tomorrow and pick the guess brain there. I already have this documented through coachmen and they are the ones that sent me the additional duct at no charge.
1. Ill probably get a call into suburban tomorrow to see what they say
2. I will hit the suburban auth center tomorrow to see what they say
3 will call dealer warranty dept to see their response
4 then make a call to coachmen to get paid if there are any out of pocket expenses on my end.
There is an issue..... I just have not figured it out yet..
Pics of 2017 model with duct, and my unit missing duct. And pics of my adding one duct. Still hi limit issue. Dont know if because its not cold outside, or there is an issue of air flow or mechanical issue.
Below pic....two ducts where I am standing. And one in the master. None in the middle of the camper. That t stat will never get satisfied....
Ill probably add the 5th duct. IMO add all the ducts you can out of your plenum....
I will add the 5th duct nect to the other I installed under the couch.