I would like to troubleshoot an apparent electrical problem in my Forest River Sierra 5th wheel RV. The furnace is

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Customer: I woud like to troubleshoot an apparent electrical problem in my Forest River Sierra 5th wheel RV. The furnace is tripping a circuit breaker (like the small car circuit breakers: a 15 amp breaker). Now it has gotten to the point that I can't even insert a breaker without it sparking and breaking the breaker before it's even snapped into place.
Answered by gene in 13 hours 13 years ago
28+ years of experience

1,036 satisfied customers

Specialities include: Auto Body Technician, Heavy Equipment Repairs, Heavy Duty Engine Repairs, Brake and Transmission Repairs


What type of furnace is this?

What is the voltage?


This furnace is from the Suburban Manufacturing Company. I guess it's 12 volts. I don't know where to find the model number, but the paperwork for it lists models SF-20, SF-25, SF-35, SF-42, SF-20F, SF-25F, SF-30F, and the SF-35F.
Hi Brian,
I think sirsparks sent this over to the RV section.
If there is a service door outside for the furnace,remove the cover,you will see the wiring going to the furnace,disconnect the red power wire,try a fuse,if it still blows the fuse then it is in the wiring from the t-stat to the furnace.
If the fuse doesn't blow then the problem lies in the furnace,first check the motor,try turning the blower wheel,be sure it turns freely.
Check these things and get back to me.
Thanks for the update. I am working on it right now and will get right back to you.
It took me this long to figure out how to get the cover off. There are two red wires plugged in. One comes from outside the box and it smaller with a white wire encased with it. The other red is thicker and is connected to another small part in front. I unplugged the thicker one in front. Was that the right one?
yes,that is the 12 volt power to the furnace,the others you are revering to go to the t-stat.
I tried a 15 amp fuse and it sparked but went in with out blowing. I took it out to check and then put it back in. Is it normal for it to spark? I am not sure how to access the blower wheel.
Couple more questions.
Does the t-stat control the roof a/c as well as the furnace?
Does the heater have an access cover outside to get to the furnace or only from the inside?
The model number should be there,can you get the model number and I will get you a manual?
There was a model number on a sticker attached to the cooling portion of the unit but when I touched it with a dampened finger to clear the dust it vanished into a smudge. I could not find a separate model number for the furnace unit. The paperwork that came with it does list model numbers as Suburban Manufacturing Company SF-20, SF-25, SF-35, SF-42, SF-20F, SF-25F, SF-30F, SF-35F, and SF-42F.

The thermostat does control the roof AC and the Furnace.

There is an outside panel that gives access to the electrical.

The panel under the refrigerator opens to reveal the furnace itself. It is encased in aluminum and with the front panel off I can see inside but I can't reach a fan.
Ok Brian,
Here is what I have on the sf series furnaces.
This is another manual.
These manuals show you how to test each component,sequence of operation,print them out for further reference.
The furnace will have to be pulled to see what is wrong,You can slide the heater out of the case by disconnecting the LP line,remove the screw in the front center, disconnect the wires and tag if you need to and slide it out of the case,now you can check the motor,if the motor is locked up,you can't spin the blower wheel.
On these models I've seen the combustion wheel,located in the small housing opposite the large blower wheel be seized in the case from improper alignment,it will melt itself to the case,free it up and realign it.
Let me know,we will go from there.
Thanks for you help. I will be back to you soon.
I will wait to here from you
OK. This thing is beginning to irritate me. To start with it is an SF-30F if that helps.
It would appear that the cabinet was installed after the heater because the heater cannot be lifted over the lip of the cabinet without running into interference from the top of the housing unit which is fastened down to the floor. I would try to loosen the base housing screws but the furnace now will not go all the way back in because something is hitting in the back.

Also, I disconnected the gas line, but it looks like I will need to take off the elbow ( which is stuck) to gain clearance on the right side. But, as I said, even when I get the elbow off, the front triangular foot of of the furnace will not clear the lip of the opening by a long shot.

I guess I need help figuring out how to push it back in far enough to undo the base of the housing unit so that maybe the whole thing will come up far enough for me to get it out.

Then theres always my jigsaw.
On the outside is the exhaust vent,pull it and the furnace will slide back in.
The box should have a cut out for the elbow to slide out after the lp line is removed,after you pull the outside vent,pull the screws holding the box,this will allow the furnace to lift up and clear the cabinet.
The smart engineers that design these units never have to work on them.
With this you should be able to slide it out of there.
Good. I got the furnace out. I blew it off. The fan spins without interference. Now what?
check all the wiring be sure there are no wires loose or shorting out.
If the wires are long enough to hook the furnace back up without reinstalling it,hook them back up and see if the fuse does not blow and if the blower starts.
Let me know
One thing I did notice when I was unhooking the red wire is a blue wire going nowhere. Does that mean anything?
the wiring is as follows
Red is 12 volt positive
Yellow is negative
The two blues go to the t-stat wiring,should be two small wires coming from the t-stat,don't matter which one goes to these.
If the blue was laying loose and touching metal it will cause a short if the t-stat was closed and sending power through.
If you can connect the wiring without installing the heater and it works then that was probably it.
The heater should be pulled and blown out as needed as you did to be sure it is not full of lint and build up on the large blower wheel,this will prolong motor life and keep the sail switch operating properly.
OK. The heater is blowing all right and now I'm thinking that that wire might have been intermitantly touching metal causing the short. But I can't figure out where it is supposed to be going or if it is an extra lead for something I don't have. Should I just wrap it in electrical tape and put it all back together, hook up the gas and see if it fires up and blows warm air?

PS Is it normal to see a spark when installing a fuse?
The fuse for the furnace is more than likely supplying power to something else as well,that is where the spark is from when you install the fuse.
There should be 4 wires coming out of the wall that hook to the furnace,a 12 volt supply,a ground and two thin wires for the t-stat one blue wire to each of the two thin t-stat wires.Reinstall and test it let me know.
The lock nut on the gas line will not thread tightly onto the elbow. It pops off every time I try to tighten it up. Of course I'm trying to be sure its seated squarely before I screw it down and it just won't tighten. Next stop? An elbow at Home Depot or what?

The blower does blow.
The line got bent a little,try to get the nut started then square the line to the nut,it happens to me all the time and it is frustrating,but the threads should be ok.
Be sure and soap the fitting after and check for leaks.
This nut will not even begin to seat itself. I understand about getting it started and wiggling the tubing to square it away and to tighten it up, but this one just will not get itself started with any thread grabbing at all. It might appear to be started but onegentle tug breaks it loose verifying that it was never really started.
Quick fix Brian,the first thread probably got crossed,with another 3/8 flare fitting run it into the nut and clean the threads,then hook it to the furnace,otherwise you need to replace the flare nut and re flare the tubing.
Thanks. I havelooked and I can't find another fitting the right size. I am going to try buying another one if I can't fix the old one. I'll take it off and go to the hardware store with it. I'm not sure how to re flare the tube end.
You will have to purchase a flaring tool,home depot carries them in the plumbing tools.
I would purchase a 3/8 flare plug and use it to clean the threads on the existing flare nut first.
OK. I'm going to the store and taking the wife to the doctor. I will be back in touch in a couple of hours. Thanks for all your help. Just respond so I have the ball back in my court.
11PM We were late getting home because we went to the doctors and ate. I got a 3/8 inch plug then realized when I got home that it wasn't a flared plug; went back and got the flared plug and it did rethread the nut well enough to seat it properly and now it's tight. The blower is blowing well. The furnace is sparking but is not igniting. The propane seems low; so maybe the gas pressure isn't high enough to facilitate ignition?

Taped the hanging blue wire presuming it to be the culprit. Without any apparent place to plug in I'm thinking that it may have slipped out of a thin band of tape that was holding some other wires in place (with it).

Does that sound plausible?

Could the blue wire have been doing nothing and just shorting the furnace? I can't see anywhere that it came out of.

You did a good job helping me. Thanks. Just check in with me tomorrow and I'll authorize payment after our last communication.

how many wires are coming out of the wall and what color are they?
You need to light the burners on the stove to bleed the air out of the system,leave them burning,turn on the heater and see if it lights.
Good news. It is blowing hot air! Leaving the burners on did the trick.

The wires I'm refering to have yellow , white, and blue. They plug into the little circuit board in the upper right hand corner. The yellow and white are being use while the blue is not. It doesn't seem to be of a length to plug in anywhere obvious and, as I said, it may have originally been taped up out of the way. You think?
If it is working and turning on and off by the t-stat,all is good,be sure you tested for leaks with soapy water at the lp line,don't want any leaks.
Thanks. You did a great job.
Thanks,glad I could help,go through the manuals I sent and you will understand how the furnace works and its components.In the future just ask for me and I will get it.gene40237.7775006944
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