Suburban Furnace Problem

[bevel_drive]

I have a 1999 Fleetwood Bounder with a Suburban SF35 furnace. Last trip, the furnace only blew cold air. I've checked the sail switch, limit switch, and I'm sure the home is still flowing propane. I'm guessing that my problem is either valve or circuit board related. Since a new SF35F can be had for just over 300$, is it even worth trying to track this problem down? How long does a typical blower motor last? Thoughts?

[RV Wizard]

bevel_drive, welcome to iRV2.com. We are glad to have you join us here and look forward to reading of your adventures and experiences.
On your furnace, blower motors can last many years but is more based on hours of use. Some use the furnace heavily and other not at all.
Have you had bug screens over the intake and exhaust vents? If not you could have pest build nests inside and this can cause you problems. How electrically and mechanically handy are you?

[bunny2448]

We just had our Winnie 2006 Vectra serviced for the umpteenth time due to our continuing furnace probs. They finally resolved our prob which was similar to yours. It was, indeed, a circuit board solution, in this case the motor control board. Hope this helps you.

Barb

[discfl]

bevel_drive. I had the same problem. It turned out to be the groundwire. I had to go out and wiggle it to get it going. If the furnace does not see a flame it will just allow the fan to run till it sees it. I had to shut it down wiggle the wires and start it up. Sometimes more than once to get it going It was a real pain on my unit. Good luck

["007"]

discfl, if the ground wire is attached to frame with screw use a star washer and it will hold better. If its on the ckt board take it off and crimp the clip so it will hold better to spade connection on board. You could clean and use some di-electric grease to protect the connections.

[discfl]

Thanks 007 will do.

[bevel_drive]

Thanks all for your responses. Took it to CW in ABQ, who reported "failed sail switch." I mentioned that a continuity check indicated that the sail switch was operational, they replied that power wasn't getting through... Since I measured no resistance on the contacts, I am skeptical (and stated as much). Will put the unit back in soon and report. FWIW, the folks at CW in ABQ were very professional and responsive. Hope they saw something that I did not.

[JLeeski]

RE; My pre 2001 SF35 repair specifically....The Suburban furnace double-safety-solenoid gas valve seal inside the valve body tends to stick, kind of melt (in closed position) to the aluminum seat closest the burner manifold tube, due to excessive heat migration back to valve body when blower occasionally runs slower than normal due to low battery pack voltage, causing a mock over-fired condition, and excessive heat at the seat closest the gas valve outlet to burner. I've successfully opened-up one of these gas valves, and after close examination turned both rubber seals over on the little intricate solenoid buttons to expose fresh rubber seal surfaces, then carefully cleaned the aluminum knife-edge seats with a Q-Tip and alcohol, and then resealed the gas valve.....but CAUTION!...I would highly recommend gas valve replacement, due to possible damage to cork gasket leading to a possible dangerous LPG leak (breaking gas valve gasket seal, and then resealing gas valve is considered dangerous by trade standards and definitely not recommended), however, it's good to know what the heck went wrong in there anyway. I have not had a problem with leakage on the one I opened and resealed, and as always, an LPG leak-test after any LPG system repair, along with a combo electronic propane alarm & safety shut off solenoid valve at the RV's main LPG tank is always a good idea.......NEXT; Eliminate the 3 wire plug on ignition board, and solder wires directly to ignition board terminals (CAREFUL)....sounds intense I know, but this will eliminate the slip connector plug as a bad-connection source (which is a common failure area)..........NEXT; Replace the sail switch with a new one, it is a common intermittent fault source, that one must carefully sneak up on to actually catch in an open circuit condition, best to just replace it. Safely perform these steps and you'll usually be 100%, without future failures, until brushes in the blower motor wear-out of course........and providing your furnace blower was indeed cycling on normally, but burner was simply failing to ignite......and providing you have eliminated bug nests, bad grounds, or other obivous faults as possibilities. Often, there is more than one problem lurking at various times, confusing the novice, and sometimes frustrating even the trained Service Tech. DON'T FORGET TO CLEAN THE LINT OFF THE BLOWER WHEEL TOO. Perserverence is always paramount when dealing with these little gems.....buurrrr.....GOOD LUCK.

[RV Wizard]

Jleeski, welcome to iRV2.com. We are glad to have you join us here and we look forward to you helping us with any technical questions that arise. It sounds like you are a qualified and trained professional.
I do have one question as to why the high limit t'stat did not open the circuit to prevent over heating of the gas valve seat seal? Is the t'stat installed incorrect? Or do you think it is at the threshold of an unsafe temperature condition?

You will find we are a group of RVers that like to help each other where we can. Thank you for you help here. Good luck and keep us posted.

[JLeeski]

REMEMBER!!....SAFETY FIRST

That's a great question and observation, why didn't the high limit protect the furnace from the overheat condition?...and it ultimately does, and did in my case before catastrophe struck, but the High Limit Safety Switch isn't designed to really cycle off and on to maintain temp (and will prematurely fail if over-cycled) but rather it is there to stand by and watch and wait for a overheat problem essentially, but when the high limit does open the circuit, due to a possible high-heat/low air flow condition, say due commonly to partially depleted/weak House batteries, or even due to factory under-ducting (another problem in some RV heating systems) the Heat-Rise climbs (Heat Rise Rating is the difference between room temp and the hot air being discharged at the supply vents) and the high limit eventually does kick-off the burner, but only after your furnace turns hotter than a fire cracker, because the gas input stays the same during this low air flow condition. The furnace then will cool, and may, depending on design, repeat this hot/cool cycle until the room thermostat is satisfied, putting extra heat strain on all components, and over time this continual overheating/cooling condition, common in RV's with battery power, along with possible under-ducting, can cause fatigue and premature wear, interesting enough the Semi-soft seal material inside the gas valve closest the burner tube connection was the only one that showed a round indentation PLUS traces of what looked to be a bit of the seal material adhered to the aluminum seat, the other aluminum seat appeared clean, although it's black rubber type material had the same seemingly normal indentation. I'm not a scientist, but I concluded that a continual low air flow/higher than normal cycling heat condition, caused some sort of rubber seal material breakdown, causing only the one seal to stick closed (I had previously observed 12v power to both solenoids, but could not blow through the gas valve with a light breath of air and 12 volts applied). I guess one could install a High Limit that kicks out at a little "LOWER" temp (CAUTION...always a lower temp rating, never higher), or add extra ducting and supply vents...BUT of course, this is why "they" sell brand new shiny RV furnaces, and that just may be the best solution for many of them after lots and lots of use/abuse, and definitely another one of the many arguments to be made for coach/house batteries being kept in tip-top shape...HOPE THIS ADDS SOME USEFUL INSIGHT, and not just more RV furnace sales, and if you do buy new, consider additional ducting to lower that high Heat-Rise, sometimes caused by overly stingy; designers/installers/builders/bidders, it won't hurt a bit to add one or two more, and will actually raise the furnace efficiency a bit, and allow it to last longer......sorry for the length here.......sometimes I get carried away.....REMEMBER!!.....SAFETY FIRST.