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Old 09-15-2021, 03:42 PM   #1
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Furnace Access - 2012 Chaparral 330 FBH

I have a furnace problem I believe can be repaired with a new sail switch, but I can't figure out an easy way to get at it on the furnace. Can anybody walk me thru access? I don't see access when I remove the vent plate in the trailer.
Thanks
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Old 09-15-2021, 04:07 PM   #2
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Can you post a picture of the cabinet where the furnace is located on the inside and the ports on the outside of the RV?

Some furnaces can be removed from the outside of the RV, but most require removing a louver or even a cabinet panel to access the furnace for removal.
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Old 09-15-2021, 05:12 PM   #3
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2012 Chaparral 330 FBH

I hope the pic comes through. On the outside of trailer all I have is the one exhaust port and no fresh air port. On the inside the vent panel is under the oven and when I open it all I see is the side or back of the furnace. When I look at it I can't see an easy access and am afraid the oven may need to come out. Click image for larger version

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Thanks for your help
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Old 09-15-2021, 08:56 PM   #4
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Is there a door on the outside of the RV where the furnace is?
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Old 09-16-2021, 08:46 AM   #5
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Unfortunately there is no access door for the furnace outside. I have one for the water heater and the frig, but not the furnace. The more I look at it I don't see any way to avoid pulling the stove and range top. Do you have any tips on doing this? I plan to disconnect the propane tanks but beyond that anything I should keep in mind?
Thanks
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Old 09-16-2021, 09:08 AM   #6
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Every RV is different so you'll have to kinda figure it out as you start removing the devices and parts. The LP gas lines to the furnace and oven/range are most likely tee'd near the appliances.

I suggest taking pictures as you go so you'll know how to put it all back together.
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Old 09-16-2021, 09:56 AM   #7
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Good point on taking pictures. Maybe I won't finish this project with an extra screw as usual!
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Old 09-16-2021, 07:15 PM   #8
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This is very easy

Quote:
Originally Posted by Kodabearra View Post
I have a furnace problem I believe can be repaired with a new sail switch, but I can't figure out an easy way to get at it on the furnace. Can anybody walk me thru access? I don't see access when I remove the vent plate in the trailer.
Thanks
This is very easy to do. (I can't imagine why anyone would suggest you remove the furnace through a 2" x 6" vent port though.)
  1. Turn off the propane at the tanks.
  2. Take off the grille inside, usually down at the floor.
  3. Turn off the propane at the tanks. (Make sure.)
  4. The propane connects to the furnace at the top right. Usually there's an elbow at the furnace, to which the furnace connects with a flare fitting. Unscrew the flare fitting. (I sometimes use a ratchet, extender, and crowsfoot socket, but you may have enough room to use a simple open-end wrench or flare wrench.)
  5. Take off the front cover of the plenum. It's usually just one or two sheet metal screws.
  6. Just inside the plenum, at the bottom, is a single anchor screw; just a small sheet metal screw going through the sheet metal and into the plywood floor. Remove it.
  7. Grasp the firebox, inside the plenum, and wiggle it while pulling it towards you. Don't move it very far yet.
  8. Look for a bundle of four wires going into the furnace. There will be a lot of slack outside the plenum at the back. As you pull the firebox out, you will need to either unplug those wires (if there is a plug-and-jack in the cable) or stuff the slack wire into the plenum as you pull the firebox out.
  9. Pull the firebox the rest of the way out. The motor, impeller fans, sail switch, and circuit board will come with it.

How do you know that it's the sail switch? A lot of people get recommendations to replace the sail switch because it's the only part of the circuit the recommender understands. Only once on these forums have I actually read of a failed sail switch. There can also be insufficient airflow (same symptoms as failed sail switch) due to the return air area clogged with dog hair or the intake/exhaust ports clogged due to mud dauber nests. But you've already checked those, right?

What are the symptoms? What else have you checked?
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Old 09-16-2021, 08:12 PM   #9
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Thanks for the suggestions, I was hoping for an easier way to access the firebox.

I don't know the problem is the sail switch, but they are cheap enough I prepared to change it if need be. On the outside of the trailer I have an exhaust port but no intake, the exhaust is clear. Inside, the grille is clean and I don't see an intake port so I assume that is inside the plenum? We do have a dog so I'll check the airflow carefully.

I am assuming my problem is airflow or the sail switch because the igniter is not trying to fire. When the thermostat calls for heat the furnace goes through the purge cycle and I then hear an electronic click but there is no click-click-click of the igniter. The fan will continue blowing for a bit then the unit shuts down. The propane flow to my oven, stovetop and water heater is good so I'm confident propane supply is good. I assume if the gas valve is defective I'd still hear the electrodes sparking so that is probably not the problem. I guess that would leave the limit switch or control board if not air flow or sail switch. Does that sound about right?
Thanks again.
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Old 09-16-2021, 08:25 PM   #10
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I'd still like to see a pic of the outside of the furnace.

The ones I've seen with only one port on the outside look like the pic below. I'm sure there are others, but that's the ones I'm familiar with.

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Old 09-16-2021, 08:53 PM   #11
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Don't think so

Quote:
Originally Posted by Kodabearra View Post
Thanks for the suggestions, I was hoping for an easier way to access the firebox.
Not exactly sure what you were expecting. I suggested disconnecting the gas and removing two screws. How much easier could it be?
Quote:
Originally Posted by Kodabearra View Post
I don't know the problem is the sail switch, but they are cheap enough I prepared to change it if need be. On the outside of the trailer I have an exhaust port but no intake, the exhaust is clear. Inside, the grille is clean and I don't see an intake port so I assume that is inside the plenum?
Umm, bad assumption. I have never seen an RV with an exhaust port but no intake port. If the intake port were inside and the exhaust outside, you would be trying to exhaust all your newly-warmed air and draw cold air through any leaks. Does your vent look like the picture below? One of those two tubes is intake and one is exhaust.
Quote:
Originally Posted by Kodabearra View Post
I am assuming my problem is airflow or the sail switch because the igniter is not trying to fire. When the thermostat calls for heat the furnace goes through the purge cycle and I then hear an electronic click but there is no click-click-click of the igniter. The fan will continue blowing for a bit then the unit shuts down.
Bad guess, I think. The electronic click you hear is the gas valve solenoid opening. You are not hearing the sparks from the Direct Spark Ignition. For proof of this theory, go outside and sniff the exhaust port while someone else exercises the furnace. You should smell propane. If it were a sail switch problem, the control board would never open the propane valve.

There are a couple of reasons that the Direct Spark Ignition wouldn't fire:
  • High-tension wire pulled off connector (It's the wire with the thick red insulation.)
  • High-tension wire pinched or cut, hence shorting to ground
  • Spark gap too wide--spark can't jump.
  • Bad control board
Really need to pull the Suburban maintenance manual--it's in the Library on this site or easily found with a Google search. You will need to pull the furnace as I described to check the above. It has a little more detail than I gave.

If it makes you feel good, once you have the unit out, you can use an ohmmeter to check the sail switch.
Quote:
Originally Posted by Kodabearra View Post
The propane flow to my oven, stovetop and water heater is good so I'm confident propane supply is good.
Don't fall into that trap. That is NOT a good assumption, for two reasons.
The gas range needs much lower pressure than the water heater or furnace. It has a secondary regulator--just lift the range top that surrounds the burners and you can see it. If the pressure from the main regulator by the tanks is too high, the range will work fine and the more-tolerant water heater will work, but the furnace won't light. (You will hear click-click from the igniter and you will smell propane at the exhaust.)
Quote:
Originally Posted by Kodabearra View Post
I assume if the gas valve is defective I'd still hear the electrodes sparking so that is probably not the problem. I guess that would leave the limit switch or control board if not air flow or sail switch. Does that sound about right?
Thanks again.
Assume? Isn't that something about a donkey and two pronouns?
Yes, if the gas valve were defective, you would still hear sparking.

You can check the gas valve (as mentioned above) by going outside and sniffing while someone else starts the furnace. Remember, it will blow for ~10 seconds before the gas valve opens to clear a charge from a previous attempt.

You can check the limit switch by jumping across it. It sits right at the top, front edge of the plenum, near the screws that hold the front plenum cover on.

You really should be considering only three things:
Where the spark is generated--on the control board
Bad wire from control board
Too big a spark gap in the firebox. (Maintenance manual tells how to set this)
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Old 09-16-2021, 10:10 PM   #12
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I appreciate the in depth post on what to look for. When I said I was looking for an easier way to get at the furnace you gave it to me, I was afraid the stove had to be removed.
As for the exhaust port mine is only a single port. I'm not at the trailer now or I would take a picture, but it is single with no access panel.
I did not smell gas when I tried to start the furnace but will double check that before i start to pull it out.
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Old 09-23-2021, 10:34 AM   #13
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Finally back at my trailer ready to pull the furnace. Attached is a picture of the exhaust port you asked to see.
Thanks

Click image for larger version

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Old 09-23-2021, 02:25 PM   #14
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That's the same furnace that I posted in #10 but without the outside access door.

If you look at the port you have, you'll see that it has both combustion air intake and exhaust. The round center port is the exhaust and around that is a square deflector which is the fresh air intake.
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Old 09-23-2021, 03:17 PM   #15
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I've disconnected the gas and vents on my furnace and am ready to pull it, but there are no quick disconnects to the 2 thermostat wires and 12 volt + and -. I've labeled them and ready to cut them unless anyone has a better and correct way. I plan to cut then put disconnect on.

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Old 09-23-2021, 08:08 PM   #16
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Next steps

Quote:
Originally Posted by Kodabearra View Post
I've disconnected the gas and vents on my furnace and am ready to pull it, but there are no quick disconnects to the 2 thermostat wires and 12 volt + and -. I've labeled them and ready to cut them unless anyone has a better and correct way. I plan to cut then put disconnect on.
If there is enough slack in the wires, you can pull the assembly out. If not, here is what I have recommended in the past.

Get a trailer 4-wire extension cable like this one. It can be short, but it should be flat cable like this one. Cut it in half, right in the center.

One plug has three embedded contacts and one exposed contact. That end will connects t +12, ground, and the two thermostat wires. Make sure that ground connects to the exposed pin.

The mating plug has three exposed pins and one embedded contact. That end connects to the furnace.

Plug the two halves together. What you will do is, one wire at a time, cut the wire and connect the two new ends to opposing wires in the connector. When you are done, you will have a four-contact disconnect. You could use solder and shrink tubing (don't forget to slide the tubing on first), or barrel crimp connectors to make the eight joints.

This is a little fancier than some other options, but it guarantees that you (or someone else) will never re-plug the furnace incorrectly.

Another topic:
The "plenum" is a sheet metal box that surrounds the firebox. It has several four-inch ducts coming out. It will stay in place when you pull the firebox out. The plenum has several "knockouts", places where the installer can pop out a four-inch circle and connect a duct. Every open knockout should have a duct. It looks like you have one knockout with no duct. Unless you know of a good reason for it, it probably should be closed off. Maybe a scrap of sheet metal and a couple of pop rivets or hex-flange-head sheet metal screws.
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Old 09-23-2021, 08:22 PM   #17
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Thanks for the tip on wiring. The knockout in the picture had a vent attached. The picture is of the side of the unit because I had to rotate it to get to wiring. My problem now is it won't slide out the opening. The propane feeds the unit with a hard pipe on top of the unit. The pipe sitting on the plenum are taller than the opening by about 3/4". I'm thinking easiest thing to do is enlarge the opening since the grill overlaps by an inch or so all around.
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Old 09-23-2021, 09:15 PM   #18
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Photo again?

Quote:
Originally Posted by Kodabearra View Post
Thanks for the tip on wiring. The knockout in the picture had a vent attached. The picture is of the side of the unit because I had to rotate it to get to wiring. My problem now is it won't slide out the opening. The propane feeds the unit with a hard pipe on top of the unit. The pipe sitting on the plenum are taller than the opening by about 3/4". I'm thinking easiest thing to do is enlarge the opening since the grill overlaps by an inch or so all around.
Post a photo of the plumbing. It's possibly blocked in, but I'd like to see it.
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Old 09-23-2021, 09:32 PM   #19
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Attached is the propane connection. In this picture the unit is sitting about a half inch lower in the cabinet.

Click image for larger version

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Old 09-23-2021, 10:05 PM   #20
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sail switch.

if you slap you hand on top of furnace cover it will jiggle the sail switch loose if it is stuck .may have to do it more than once. fixed mine .sounds like a joke but it does work.
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