Need help to access furnace

[Desdinova]

Is there a secret way to access the furnace for maintenance on a 26RK? The hatch from the bedroom on mine reveals nothing but the sealed bottom of the unit. All hoses, wires, lines, vents are facing the back of the shower. It like the installed the wrong furnace, or the correct one the wrong way.

Unless there is another secret passage.

Honestly, it looks like they installed a furnace and built a trailer around it.

FWIW, I think my sail switch failed.

[KyDan]

Bump- anybody??

[Mr. Dan]

I don’t have the same unit but I have a rectangular louver/grate under my refrigerator where my furnace gets its return air to reheat. I just remove that intake grate and I can see my furnace.

[Bama Rambler]

I assume this is a Vibe 26RK and not a Jayco White Hawk 26RK?

There is a way to get to the furnace but it requires some dismantling of the cabinet. And some contortionist ability on the part of the tech doing the work.

You need to remove the return air panel from the side of the cabinet and you can access some of the screws by contorting around in there, then you need to open the cabinet door on the other side and clean out the cabinet. I don't remember if there's a panel at the back of the furnace in that unit, but there is in some. If there is you'll have to remove it to access the back of the furnace to remove the mounting screws. There can be screws and/or staples holding the partition in.

[Desdinova]

Where is says "ward" in the bedroom is where the furnace is.

[Bama Rambler]

I was looking at a different model without the outdoor kitchen. Which year is yours?

[Scrapper]

The floor plans hardly ever show where the furnace is. Look for a slotted panel on a cabinet wall at floor level. The furnace needs access to the outside air so the panel will be near an outside wall. Pictures of return air vents attached.

[Larry-NC]

Originally Posted by Desdinova

Is there a secret way to access the furnace for maintenance on a 26RK? The hatch from the bedroom on mine reveals nothing but the sealed bottom of the unit. All hoses, wires, lines, vents are facing the back of the shower. It like the installed the wrong furnace, or the correct one the wrong way.

Unless there is another secret passage.

Honestly, it looks like they installed a furnace and built a trailer around it.

FWIW, I think my sail switch failed.

I am assuming this furnace is the ubiquitous SF-series Suburban. The numbers after the SF- just indicate the KBTU rating. Installation and maintenance are the same on all of these.

Here is how you access it:

• Turn off the gas.
• Take off the return air grill.
• Turn off the gas.
• In your case, you may also have to remove the mattress and plywood under it, and maybe a cabinet door. I cannot tell.
• You will see the plenum, a sheet metal box. It has some vents on the side, but the front is blank. You will leave the plenum in place, and pull the guts out of it.
• Remove the two screws at the top of the blank front and remove the front.
• Turn off the gas.
• Disconnect the gas line at the flare nut. Sometimes this requires unusual tools. I have had to use a crowfoot socket or a crowfoot flare socket.
• Now inspect the wiring. There are three cases:
  1. Wiring has connectors so you can disconnect the furnace from the 12v, ground, and thermostat.
  2. Wiring is long enough that you can stuff excess wiring into the plenum as you extract the furnace.
  3. Wiring is too darn short. See instructions for this case below.
• Modify wiring as needed.
• There will be one anchor screw at the front bottom center. Remove this screw.
• Pull the entire furnace guts out. It will take a little jockeying.

What if the wiring is too short?
You could Label the wires on both sides of your cut, the cut the wires and reconnect them later
You could cut the wires one at a time and splice in a couple of feet of wire on each
My preference. Buy one of these. Cut it in two, right at the center. Now you have a nice set of connectors with pigtails. Figure out which of the four wires is ground. Cut that wire. One of the connectors has one exposed contact and one has three. Take the connector with one exposed contact and connect the incoming ground wire (not the one going to the furnace) to it. Plug the two connectors together and connect the ground going to the furnace to the corresponding contact. For each of the other wires, one at a time, cut, then connect the two ends to corresponding contacts on the connector pair. When you are finished, you will be able to unplug the furnace when you take it out.

What about putting it back?
Putting it back is very straightforward except for the first step. When you pulled the furnace out, you noticed that you separated the air intake and exhaust tubes from their mating tubes on the exterior vent. When you slide the guts in, you will have to wiggle and jockey the unit around until the tubes mate. It might take a while. Only as a last resort should you remove the exterior vent. You will need some butyl tape to seal the vent to the trailer if you remove it--and it's a messy job. All the rest is just reversing the steps above.

Is it really the sail switch?
When the furnace doesn't work, it seems like some folks always leap to the conclusion that it must be the sail switch, possibly because that's the only part they understand. The sail switch is a standard "microswitch" that is rated for hundreds of thousands of operations. I've been following these forums for a while and I don't remember any instances where it actually was the sail switch.

If the sail switch is not closing, there are several causes besides switch failure. First, is it not closing? When you call for heat, do you hear the fan run for several seconds and then stop without ever hearing the propane valve solenoid open (click) and the spark ignition (snap) several times? If, indeed, that is the case, it is likely that there is insufficient air flow to the furnace.
One cause is a low battery. The fan is a DC motor; speed is proportional to voltage. If the fan is not running fast enough, you will get the symptom described above.

Another cause is restricted air flow. The fan motor is double-ended. There is a squirrel cage blower on each end. One blower draws air from the exterior intake vent, blows it through the firebox and out the exhaust vent. The other blower draws air through the return air vent (first thing you removed), blows it through the plenum surrounding the firebox and out the heating vents. If you accidentally covered a vent with a floor mat or replaced the grilles with adjustable grilles, you could restrict the air sufficiently to get this symptom.

Another cause could be pet hair or other substance. There is no return air filter in this system and Suburban cautions against using one--for just this problem (and another one). I suppose that enough pet hair could restrict return air and restrict sufficient air flow to cause this symptom. But I have pulled out pounds of hair from ours and never seen this happen. (DW full-timed in the trailer for six years with really shaggy Aussies.)

Let us know what you find.

[Scrapper]

Originally Posted by Desdinova

Where is says "ward" in the bedroom is where the furnace is.

Looking at the exterior view of a 2020 Vibe 26RK the water heater is under the bedroom wardrobe and furnace is on the side just in front of the slideout. So according to the floor plan you give us the furnace is in the entertainment center next to the fireplace.

What I find confusing is the 360* walk-a-round view shows the cold air return intake in the sink cabinet next to the chair. The furnace is always located behind the cold air return. The cold air return will be large because it needs to be at least 55 square inches up to 30kbtu furnaces, 113 sq inches for 40kbtu furnaces, and 142 square inches for 42kbtu furnaces.

Attached is the service manual for Suburban furnaces with all the information you need.

[Larry-NC]

Originally Posted by Scrapper

The furnace is always located behind the cold air return. The cold air return will be large because it needs to be at least 55 square inches up 30kbtu furnaces, 113 sq inches for 40kbtu furnaces, and 142 square inches for 42kbtu furnaces.

Usually behind the vent. Not always. Our SOB has one (small) vent directly in front of the furnace and a larger vent under the next cabinet. Someone thought it was a good idea to draw dusty air through the under-sink cabinet.

[Scrapper]

Originally Posted by Larry-NC

Usually behind the vent. Not always. Our SOB has one (small) vent directly in front of the furnace and a larger vent under the next cabinet. Someone thought it was a good idea to draw dusty air through the under-sink cabinet.

That's what happens when you buy SOB.

[Larry-NC]

Originally Posted by Scrapper

That's what happens when you buy SOB.

Not my decision. DW bought it and full-timed in it (22-footer) for six years before I met her. We call it her "dowry."

[Desdinova]

Just so ya'll know that I know my left from right and the difference between a water heater and a furnace, here is the closet in the bedroom with the shelves removed. There is no other access. This wasn't too bad actually. 6 screws to pull the top shelf, and the bottom one was only stapled down so it popped out. I'm actually going to make it just one shelf, hinged for future access.

Unfortunately, I'm going to have to pull the unit for any testing. This is the same furnace style that was on my previous trailer and the only way to troubleshoot beyond it being hooked up, is to slide the chassis out of the case, which can't happen in its current location.

Just need to take off the vent from the outside. And two screws on the inside are all thats holding it in place.

Honestly, under the kitchen sink, or even under the fridge would be better locations. Or, a different model furnace that has access on the opposite side

[Desdinova]

Pm

Originally Posted by Larry-NC

Is it really the sail switch?
When the furnace doesn't work, it seems like some folks always leap to the conclusion that it must be the sail switch, possibly because that's the only part they understand. The sail switch is a standard "microswitch" that is rated for hundreds of thousands of operations. I've been following these forums for a while and I don't remember any instances where it actually was the sail switch.

If the sail switch is not closing, there are several causes besides switch failure. First, is it not closing? When you call for heat, do you hear the fan run for several seconds and then stop without ever hearing the propane valve solenoid open (click) and the spark ignition (snap) several times? If, indeed, that is the case, it is likely that there is insufficient air flow to the furnace.
One cause is a low battery. The fan is a DC motor; speed is proportional to voltage. If the fan is not running fast enough, you will get the symptom described above.

Another cause is restricted air flow. The fan motor is double-ended. There is a squirrel cage blower on each end. One blower draws air from the exterior intake vent, blows it through the firebox and out the exhaust vent. The other blower draws air through the return air vent (first thing you removed), blows it through the plenum surrounding the firebox and out the heating vents. If you accidentally covered a vent with a floor mat or replaced the grilles with adjustable grilles, you could restrict the air sufficiently to get this symptom.

Another cause could be pet hair or other substance. There is no return air filter in this system and Suburban cautions against using one--for just this problem (and another one). I suppose that enough pet hair could restrict return air and restrict sufficient air flow to cause this symptom. But I have pulled out pounds of hair from ours and never seen this happen. (DW full-timed in the trailer for six years with really shaggy Aussies.)

Let us know what you find.

My reasoning to think sailswitch although it could be a bad control board, is exactly as you state, but there is nothing blocking flow. Its a new trailer, I couldn't even find dust in it. It was working fine until it wasn't. But i will post when I figure it out.

Unfortunately, as previously posted, I need to remove the unit for any more serious diags.

[Larry-NC]

Originally Posted by Desdinova

My reasoning to think sailswitch although it could be a bad control board, is exactly as you state, but there is nothing blocking flow. Its a new trailer, I couldn't even find dust in it. It was working fine until it wasn't. But u will post when I figure it out.

Unfortunately, as previously posted, I need to remove the unit for any more serious diags.

I'm wondering what model number the furnace is. Is it an SFV-series instead of an SF-series I'm most familiar with? From your photos it looks like an SF-series standing on its back face so I was wondering if it's an SFV.

Keep us posted and good luck.

[Desdinova]

Originally Posted by Larry-NC

I'm wondering what model number the furnace is. Is it an SFV-series instead of an SF-series I'm most familiar with? From your photos it looks like an SF-series standing on its back face so I was wondering if it's an SFV.

Keep us posted and good luck.

I can't read the model number yet, but the unit is on it's left side.

[Desdinova]

It's an SF-30Q and here's where it gets interesting....

Got the unit out, put it on the bench, tested the switch, the thermostat, the relay, checked all wires, hooked up to a portable tank, and it worked..

I recycled it several times. I did check the gas line on the rig as I was taking it out, and there was gas... at the furnace, so that's not it.

Something was stuck, but if it got stuck once, something tells me it will get stuck again.

One cool observation is there really is one of the duct vents open to the belly of the rig. 2" hose goes down there. In my case it's near the grey and black tanks, but I'm sure the whole undercarriage stays toasty when it's on. I guess the tank heaters are probably for when not using the propane heat, or just added saftey. Anyway, thought that was pretty cool.

Now back to my head-scratching.

[Larry-NC]

Originally Posted by Desdinova

It's an SF-30Q and here's where it gets interesting....

Got the unit out, put it on the bench, tested the switch, the thermostat, the relay, checked all wires, hooked up to a portable tank, and it worked..

I recycled it several times. I did check the gas line on the rig as I was taking it out, and there was gas... at the furnace, so that's not it.

Something was stuck, but if it got stuck once, something tells me it will get stuck again.

One cool observation is there really is one of the duct vents open to the belly of the rig. 2" hose goes down there. In my case it's near the grey and black tanks, but I'm sure the whole undercarriage stays toasty when it's on. I guess the tank heaters are probably for when not using the propane heat, or just added saftey. Anyway, thought that was pretty cool.

Now back to my head-scratching.

Okay...here is where I confess my stubbornness. We had an issue with the SF-25 in DW's 22-footer. It wouldn't light although there WAS spark and gas. The sail switch was obviously working.

The first step in the troubleshooting manual (easily found online) is to check the pressure from the regulator. I didn't have a manometer so I skipped that step. Later steps included tearing the furnace down, cleaning both impellers, cleaning out six years of dog hair, checking all connectors, and a bunch of other things, even cleaning the firebox as best I could. After each attempt, I re-installed the furnace so I could re-connect the gas. It wouldn't ignite.

Then (I don't know if you could do this) I happened to slide it in place and re-connect the gas and attempt to start it without the front plenum cover on. That meant that one squirrel cage blower was pumping air through the firebox as it should, but the other blower was pumping air straight out the front of the furnace at me instead of through the ducts. I was instantly awash in a torrent of hot air! Lowering the air resistance of one blower meant that the motor was running at a different speed, changing airflow rate through the firebox. (It's counter-intuitive, but when you increase air flow resistance, the motor speed increases, not decreases.)

I figured out that there had to be a different rate of air flow through the firebox with the different speed--so the fuel-air ratio was wrong. And that's when I had the AHA moment that maybe I ought to go back and check the propane pressure. The specification is Min. 11” W.C.*, Max. 14” W.C. Those measurements are inches of water column, both are around 1/2 psi. The pressure gauge you use is called a manometer. At the time, the only pre-made ones cost around $50, and I wasn't really sure this would help, so I reverted to basic physical principles and built one following directions I found in some RV forum. It cost about $5 for a yard of tubing and two fittings. The rest was scrap I had around the house. It took about an hour to construct. See the picture.

The manometer was filled to the 0 mark with water and a few drops of blue food coloring for visibility.

I disconnected the furnace and connected the propane line to the manometer. While I was inside watching the manometer, my buddy turned on the gas. Sure enough, the pressure was out of spec. It was 16" if I recall correctly. The regulators are adjustable, but as soon as we touched the screw, the regulator began hissing. The rusty diaphragm which had a pinhole leak disintegrated at the first attempt to adjust it. That's when I learned that most folks have to replace the regulator every 8-10 years for this failure mode. I had wasted hours of time by not following all the troubleshooting steps in order.

[Desdinova]

Originally Posted by Larry-NC

Okay...here is where I confess my stubbornness..

We must be brothers from other mothers..

So I get my "working" (term used loosely) furnace back into the rig. I test it, it's fine. I'm tidying up the wires and it "cycles" off. WHat huh? It's not 75 degrees in here yet (where I had the thermostat set)..

But how can it be the thermostat... I eliminated that by jumping it at the furnace... so I did that again, and NO SPARK !!! Arrrrgghhh back to zero.

I took the furnace out, put it on the bench, did the same things I did about an hour ago, and it's not firing.

To be clear... I get 30 seconds of the blower, and it shuts off. No attempted ignition at all. Not three times, not once.

I'm using a stand-alone tank and regulator for testing which I have used before and all of the other gas appliances on the rig seem to be fine, and in fact, even the furnace was working for a bit after the re-install unilt it wasn't.

I'm thinking it's something intermittent, and the only thing I can think of is the control board is faulty at this point.

[Larry-NC]

Originally Posted by Desdinova

To be clear... I get 30 seconds of the blower, and it shuts off. No attempted ignition at all. Not three times, not once.

That is the exact behavior of a failed sail switch (or related circuitry on the control board). And one of the failure modes of a switch is intermittency--even a situation where non-conductive contamination intermittently gets between the contacts.

Since you have failure on the bench, you could jumper the Common (C) and Normally Open (NO) terminals and give it another try.

To test the contamination theory, you could remove the switch and shake it a bit while clicking it, in various orientations--maybe rap it a bit on various sides--to displace the foreign body. I've done that to fan switches on our trailer.

DC is much harder on switches than AC. It's why you so often see a switch with ratings like:
AC: 120V 10A / DC: 24V, 2A
In repeated DC operations, the arcing at opening/closing transfers contact metal from one contact to the other. Eventually all the contact metal is gone from the donor contact. In AC operations, half the time the transfer is in one direction, half the time in the other, so there's no net loss to either contact.

I've noticed that several of the failed switches in our trailer have been used in applications beyond their ratings but I don't think that's the case on the sail switch.