Suburban Furnace Troubleshooting

CrazyCooter

Well-known member
Since the rig was new, the furnace has been really noisy at start up, but figured it was just because it was much larger than my last unit.

Sometimes everything is normal, but more times than not, the blower starts, then the gas valve opens and will ignite. It then sounds like a jet powering up for takeoff and vibrates the floor and cabinets. Sometimes it take 2 or three tries for it to ignite, but this last trip it was in the low 20's at night and I would wake up cold and the furnace failed to light. I would then reset the thermostat and try again before going back to bed.

I have a screen over the inlet/outlets, but it had this problem before I installed it. I have tried a separate tank/regulator combo with the same results.

It really sounds like it is a lean fuel condition due to the violent nature of the hum followed by the flame going out, but I'm no appliance mechanic either....
 

danemayer

Well-known member
Hi CrazyCooter,

I found the following guidance that applies to older Suburban furnaces. Not sure if current models are the same.

A symptom of too much primary air will be a howling or screeching noise when the
burner is on. Reduce the air by turning the adjustment screw counterclockwise.

I'm not sure how you would get to the adjusting screw, and it's dangerous to run experiments on gas systems. So this might be something best left to a trained technician.

You probably have a 2 year warranty on the furnace, so Suburban may cover the repair.
 

CrazyCooter

Well-known member
Thanks for the quick response! Guess I should pull the access door off, get the model#, and then download the service manual. It would be nice if it was a simple adjustment.

Everything is out of warranty by now, but I do have an extended warranty if it is something serious though. I do know a few RV techs too.
 

57chevyconvt

Well-known member
Since some spiders like to whiff propane, a spider web could be interfering with the 'sail switch'. The sail switch has to satisfy air flow requirements before the gas valve will open for ignition. Had this problem on SOB even though I had a bug screen over the inlet and outlet air vents. Removed the unit from the sheet metal housing and took it to a local deal for them to do a bench test of the unit and ultimate solve the problem.
 

CrazyCooter

Well-known member
I took the cover off and it is a model SF35Q.

The sail switch seems to be functioning as it should. It always lights initially, but after howling and sputtering, it sometimes goes out and tries to relight again. After the third try I guess it goes into some kind of error mode?

It works fine here in the back yard with the cover off! Maybe leave the screen off again and see how it does on the trip in two weeks.....I always have the catalytic heaters for most of the heat needs anyway. I just use the furnace to circulate the air and bring temps up that last deg or two.

Maybe it's the extreme cold it doesn't like?
 

sjs731

Well-known member
I had the same problem on our last trip for the year. Unfortunately I just stored the rig yesterday and saw this post this morning. I'll have to check it in the spring. I would get the "jet engine howl" on first try and it would light fine right after that.


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brianharrison

Well-known member
I took the cover off and it is a model SF35Q.

It works fine here in the back yard with the cover off! �

Maybe it's the extreme cold it doesn't like?

Just a thought, but is there a possibility fuel supply is restricted with debris (wax/oil) in the supply lines/regulator that gets worse with cold ambient temps?

Brian
 

123camper

Well-known member
We had the same problem on an old class c we had years ago. I took the furnace apart and found a mud dobber had made its home in the burner. It took some doing but I finally got it all cleaned up put back together and it worked fine after that.
Gary
 

CrazyCooter

Well-known member
Just a thought, but is there a possibility fuel supply is restricted with debris (wax/oil) in the supply lines/regulator that gets worse with cold ambient temps?

Brian

That is my guess if the obvious checks out. I was thinking there may be a screen on the fuel valve inlet that was partially plugged with sealant or other construction debris.
 

CrazyCooter

Well-known member
We had the same problem on an old class c we had years ago. I took the furnace apart and found a mud dobber had made its home in the burner. It took some doing but I finally got it all cleaned up put back together and it worked fine after that.
Gary

I have seen that first hand as well, but I took delivery of this unit within 1 week of completion and there has been a screen on it since the day it was delivered. Still a possibility, but unlikely.

Been thinking about a weak gas valve coil that get weaker with cold temps.....

I'm going to run it without the screen and see what happens.
 

brianharrison

Well-known member
Been thinking about a weak gas valve coil that get weaker with cold temps.....

I believe the gas valves are on/off; not regulating. I am thinking a weak coil would not open at all. Somewhere out there in internet land there should be a resistance value for a good 12V coil.

Brian
 
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