Furnace trouble again .....

[xtal_01]

I don't know what I did wrong this time ....

So back to the 1999 28-T Bounder.

I put a new furnace in last year ... second time I did this .. SUBURBAN FURNACE SF-35

I had also found the safety valve was full of oil (caused low flow and furnace not to run) ... fixed.

Tried the furnace a few weeks ago ... started but only after a few tries.

Well the only thing I had not replaced was the regulator.

So I was on here a couple weeks ago and was recommended to get this one: https://www.amazon.com/gp/product/B00KTS0QDY/ref=ppx_yo_dt_b_asin_image_o03_s00?ie=UTF8&psc=1

It came in and looks very close the the original ... fit great!

Tried the furnace .... started right up!

Only "odd" thing I noticed was the regulator "singing" ... noticeable buzzing sound. I don't remember my old one doing this.

The noise "could" also be the flow limiter right before the regulator .... part of a Tee kit I put in years ago so I could feed the RV with an external tank ... the piece that screws into the regulator has what I think is a high flow shut off (think they are called velocity fuses) ... in case a line breaks and there is high flow it shuts off the line.

Hard to tell but I think it is the regulator.

Anyway ..... furnace runs for about 5 minutes then I hear the noise stop from the regulator and the flame go out .... it is no were near temperature so it is not the thermostat ... but the fan keeps running.

Then after a couple minutes, the furnace ignites again! Fan has continued to run during this time.

Then after about 5 minutes (maybe less) .... flame goes out .....

Fan still running .... a couple minutes pass ... furnace ignites again!

It does this consistently over and over again!

So what is going on ???????????????????

My best "guess" is that the over temp switch is tripping

When it cools, the burner comes back on.

I checked the vents in the RV ... clear.

I checked inlet and exhaust for bugs (I have a screen on them) ... blew it out ... clear.

Could this be it ... if the switch trips, will the fan keep running and the furnace start again when it cools ??????

If this is the problem .... why?

Bad switch? Furnace is only a year old and this has never happened before.

Why did it show up when I changed out the regulator? More propane now so it is getting hotter?

Bad regulator giving too much pressure?

I am not sure what to do ... I need to get this fixed in a few weeks .....any suggestions????

Also, if it is the switch, which one is it ... I see a few different ones out there listed for a SF-35

Another "also", I did check the stove burner ... goes super low with no problem ... on high it seems to have a slight pulsation to the flame (just slightly ... high .. a bit lower ...high ... a bit lower) ... not much but something I noticed.

Thanks ..... Mike

[xtal_01]

Hmmmm .... I honestly hope this is true .... problem solved.

The factory really didn't want to talk to me. Got a woman who really only said the minimum she had to.

As I said, she said it should not cycle ... the switch is just an emergency high temp shut off.

I even tried e-mailing them ... they did not respond.

They recommend a local shop .... never! Our local shop is horrible ... tried them for a few things over he years ... never ends up well. Plus they charge double to triple what I can get parts online for ... plus $120 an hour ... min 1 hour (and I mean even to change a windshield wiper).

I did clear out the oil last year when I fixed the solenoid ... was still clean when I took it off the other day.

i will check the few simple things mentioned but I might just let it go.

I just need it to work for a week or so over Christmas (always end up going to Canada to visit my family near Niagara Falls).

Long story but this RV has been a real learning experience. I met my present partner 10 years ago (another long story ... I was a widower living in SC ... she lived in VT). She is paralyzed from the shoulders down as the result of a diving accident when she was 12 ... she is 40 now. She had not traveled because she needs care every 4 hours. She also had to stay here in VT as her job and health insurance is here. So I bought a 10 year old Bounder ... gutted the interior .... cut a new door and built a wheelchair lift (they wanted more for the lift than I paid for the RV) ... built a lift inside from front to back so I could get her out of her wheelchair and to the bed ... installed two hospital beds on tracks so they can mover side to side of be locked together as one.

We first used it on our honeymoon after our commitment ceremony.

We could not find an accessible house we could afford so we lived in it onsite for three years while I built the house ... it has been 7 years but I am "almost" done.

Next it is the workshop ... concrete pad is poured ... start building in the spring.

I have had a lot of learning on this RV ... and I am still learning!

Thanks so much for all the help and advice!

For some reason I could not insert an image but here is a link to one.

https://imgur.com/a/IVwIC7M

[goff1256]

Whoever you talk to at suburban must be new or was not a technician I have worked on RV furnaces for over 30 years it’s normal for them to cycle on and off I’ve never seen one that didn’t you can continue to work on this thing and let it drive you nuts and I’m telling you it will continue to cycle on and off for the rest of its life once you check the flow and the pressure of the regulator and clean the oil out of the lines which only usually is in the line from the tank to the regulator and sometimes in the low pressure line but it rarely gets into the appliances as they are always above The main gas line fluid does not run uphill yeah less the line is completely full which I doubt would ever occur

[dougrainer]

"Bad switch? Furnace is only a year old and this has never happened before".

Do you realize how ridiculous this sounds:B
Using this logic, AN RV OR NEW APPLIANCE WOULD Never have a warranty type problem under its warranty?????? Just because the furnace is new does not keep a Hi limit switch from failing. FYI, Hi limits DO have a higher than normal failure rate. But, they usually stick OPEN and do not allow the furnace to operate at all. Now, one thing you mentioned in your first post was the OILY substance in the area of the old Furnace solenoid. THAT should have been addressed BEFORE you did anything else. Replacing the Regulator was NOT the only thing to do. IF you have the OILY contamination, especially downstream at an appliance, Where do you think the oil came from? It came from the LP tank. It ruined the regulator and you now have that oily substance thruout your LP line system. You may need to flush your LP lines, but I would concentrate on the line from the furnace to the main pipe manifold under the RV. Doug

[xtal_01]

Great idea!

I had to do that to my house. They guy sized the intake duct too small. I left the door off the filter and it no longer tripped the high temp.

I will give that a try!

If I need to pull the furnace, I will replace the switch anyway ... they are only $5 ... probably the cheapest part I have ever bought for the RV

Thanks ..... Mike

[sundancer268]

I would disconnect the factory ducts and see if it will run longer, I am thinking the old flexible ducts are starting to restrict the air flow and the new regulator just added more heat to the heat exchanger that the old duct work can't handle so you are tripping on over heat limits.

[Chris_Bryant]

Come to think of it, that model has more than its share of bad limit switches.

[xtal_01]

I was wrong ... there is a line going to the back of the furnace ... goes under the floor to the washroom.

I guess I will try the simple things first ... check regulator, change temp switch, ...

Thanks .... Mike

[MountainAir05]

I think you found your problem . You stated no issue like this until you got a new regulator. Then a new regulator issues started.

[xtal_01]

I completely agree but .....

My problem is this is a 20 year old unit and the problem just started after I changed out the regulator.

My "feeling" was the old regulator was not supplying enough fuel ... the burner sounder like it was pulsing (whoosh ...whoosh ... whoosh) ...

It now sounds much more steady of a flame.

I have not changed any of the duct work in the RV and I checked to see if it was blocked ... it is not.

I did check the outside vents ... I installed a bug screen over them years ago ... even blew air down it .... seems fine.

I bought the unit 10 years ago and we lived full time in it for 3 years while we built a house (not fun here in Vermont).

One thing I did notice ... the factory cut a new hole in the furnace housing to install the ducts. Rather then use the factory cut outs, they cut out the top of the furnace.

It just always seemed odd to me as there is now way for the air to pass by the back of the exchanger ... the blower sends it over the top and out. If the air was exiting the back, it might coll the switch better.

As I said, I have had this unit for 10 years and it has never been a problem before but by putting on a new regulator and possibly putting out more heat, could I have discovered a problem that has been there all along?

Any suggestions on how to fix the problem would be greatly appreciated!

Thanks again .... Mike

[Chris_Bryant]

Ducting, hot air recirculating, return air.

[xtal_01]

Just called the factory ... the unit should not cycle ... the limit switch should not be tripping.

So .... I can think of three problems

1) bad high temp limit switch

2) too high fuel pressure (burning hot as it has too much fuel)

3) too low fuel pressure (burning hot as it is burning very lean)

Do any of these seem plausible?

Again, I did not see this problem before I changed regulators. I am not sure if it a regulator problem or having a new regulator just made an existing problem show up.

Anything else I should look at?

Thanks ..... Mike

[xtal_01]

Thanks!

I was just on their web site.

I tried to send an e-mail but it would not go through ... kept getting errors.

I will give them a call tomorrow.

Thanks so much !!!!!!!!!

Mike

[DFord]

https://www.airxcel.com/rv/suburban/service-support

PLEASE NOTE: Suburban Gas Appliances should be installed and/or serviced by a certified gas technician or authorized service agency. To find an Authorized Service Center near you, please CLICK HERE.
AIRXCEL, INC. - SUBURBAN DIVISION
676 Broadway Street
Dayton, Tennessee 37321
Customer Service

Phone: 423.775.2131

Fax: 423.775.7015

Service Department

Phone: 423.775.2131

Fax: 423.775.7015

[xtal_01]

Thanks .....

You guys read my mind (my wife says it is a short story) .... I was planning on heading to the hardware store tomorrow to make a manometer and check the pressure.

So you guys are saying it is "normal" for the high temps switch to cut in and out?

I thought I read on a dealer side (been searching for info all over the web) the unit should run and stay on until it comes up to temperature? The high temp switch is just that ... a safety switch. Or am I wrong?

The RV is 20 years old so for all I know the old regulator may have been failing for years and maybe I just never saw this problem as the furnace has never gotten enough fuel ... or maybe it is getting too much now ... or ????

One thing that always bothered me ... Bounder cut the furnace case and has the lines coming off the top ... not the ends or side where Suburban has holes for it ... it came this way from the factory! I was always wondering if there is the correct air flow over the heat exchange. I would think there is or everyone would have this problem.

Anyway, I guess I will check the pressure first and go from there.

Thanks .... Mike