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Old 12-13-2022, 07:25 AM   #1
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LP Heat coming from ceiling and not from floor

I have a 2011 Sightseer 35J with an Onan 5500 Generator. I will soon be traveling to Breckenridge, CO for a ski trip and know that propane heat will be our best option while there. However, LP heat is not working correctly and when I choose it on the thermostat (auto fan setting and temp as high as it will go), I get only cool air from the floor vents. Warm air does come through the ceiling vents, however - but does that mean the systems defaults to electric heat??. The generator runs just fine and when I test I am not plugged into shore power. The unit kicks on outside and air flows for a few minutes and then stops...also, I noticed that the sail switch does indeed activate. I've checked for blockages in the air intake and there doesn't seem to be anything in the way. Please help, and thank you in advance! Chris
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Old 12-13-2022, 08:25 AM   #2
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Sounds like the furnace is actually not lighting at all and any heat from above is from other sources like heating strips, etc.
The ductwork for the furnace should not be connected to the ceiling if the online info is correct.
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To verify this idea, there are two small round vents on the furnace outer side. One intake, one outlet. If you are standing out there as the thermosat calls for heat, you should hear a number of things like when the blower comes on. Check there is good airflow going in and coming out.
Possible wasp nest blocking flow?
Do you hear the fire light with a puff? If so but I suspect not, there will be really hot air coming out of the exhaust vent as the fire burns.

I suggest looking on the furnace outside for the label telling which brand and model then go online for troubleshooting manual for that specific furnace to get the best info.

Many have the same basic functions but there can be small points which vary.
General idea on many is that the thermostat calls for heat, that starts the chain like this.
Blower comes on which is a combined room air and combustion air blower.
That moves air through the combustion section, causing the sail switch to move and close.
If that sai switch closes, the circuit board starts a timer and then sends a signal to the gas valve to open and the ignition system to start. That is often a snapping sound like a gas grill makes.
If gas flows and ignites, there is some form of flame sensing which takes over and holds thing steady with the flame burning until the room temp is reached.

If any part of this fails, the fire is not lit and the system may try three times and then lockout until reset.

Some of the reallly simple things to find is corrosion on some of the leads which are plugged in on the furnace. Possible the sail switch is doing it's job but the wires on the board are corroded? Small points that one might find by just pulling any of those off and scraping/scrubbing the contacts , just as a "shot in the dark" chance!

But several of those points can be followed by listening or feeling of the parts like the gas valve.
Some "quickie" ideas there but following a real manual to get the exact rules is often best!
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Old 12-13-2022, 09:10 AM   #3
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Richard,

That's great information, and thanks so much! I will see if I can find the troubleshooting manual for the furnace and try disconnecting, cleaning, and reconnecting the leads that I see. Per your instruction, I did notice that air is flowing in and out of the vents on the outside of the RV. But, I don't ever hear the ticking nor ignition of the flame. I'll circle back after I have another chance to troubleshoot!
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Old 12-13-2022, 10:46 AM   #4
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Sounds good. The main thing to keep in mind is the way things have to happen in order and try to spot where the process stops.
One of the more frequent things we hear about is the sail switch is not getting moved enough to close and that stops the process.
It is a safety tiem that acts to keep the gas valve from being opeend when there is not good air flow to keep the gas from collecting in the furnace without being lit. That big bunch of gas can suddenly fire off and blow things up, so they set it to not get gas until the air flow is good.
One way that airflow can get restricted is when spiders, mud daubers, or wasps go in the vent tube and build a nest. Paper wasp nests can often be found built hanging down from the top and built to conform to the shape of the tube sop that air is really almost totally blocked.
One semi-easy quickie thing might be to run a wire in one vent and kind of bang around to see if you can snag a nest out. Be aware that they get offened if they are living there, so be ready to run!

And it can always be a bad board but that's the expensive thing, so no need to jump to that until we find out that it is getting all the right signals going in to it!
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Old 12-13-2022, 10:08 PM   #5
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Sounds good. The main thing to keep in mind is the way things have to happen in order and try to spot where the process stops.
One of the more frequent things we hear about is the sail switch is not getting moved enough to close and that stops the process.
It is a safety tiem that acts to keep the gas valve from being opeend when there is not good air flow to keep the gas from collecting in the furnace without being lit. That big bunch of gas can suddenly fire off and blow things up, so they set it to not get gas until the air flow is good.
One way that airflow can get restricted is when spiders, mud daubers, or wasps go in the vent tube and build a nest. Paper wasp nests can often be found built hanging down from the top and built to conform to the shape of the tube sop that air is really almost totally blocked.
One semi-easy quickie thing might be to run a wire in one vent and kind of bang around to see if you can snag a nest out. Be aware that they get offened if they are living there, so be ready to run!

And it can always be a bad board but that's the expensive thing, so no need to jump to that until we find out that it is getting all the right signals going in to it!

Actually the sail switch is to insure adequate air flow around the heat exchanger to keep it from overheating and tripping the over-temperature switch,This is a dual safety feature, in addition to the separate fan that pulls in combustion air and expels burned gas fumes as you said.
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Old 12-14-2022, 07:46 AM   #6
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Good reason for me to recommend getting the correct manual for the specific furnace being used as the devil is often in the details which are often missed when just shotgunning without knowing what we are doing.
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Old 12-14-2022, 09:33 AM   #7
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**Update** - Testing again yesterday, I listened outside the unit where the intake/blower exists and I did hear the clicking noise happen 3 times before the blower shut off. I did not however smell any LP Gas. So, it seems it's just not getting any gas to light the flame?? I also noticed a small piece of a mud-dobber nest in the intake and was able to remove that, but it made no difference. Also, just FYI...the unit is made by Suburban.
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Old 12-14-2022, 02:58 PM   #8
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Originally Posted by ccwinnie71 View Post
**Update** - Testing again yesterday, I listened outside the unit where the intake/blower exists and I did hear the clicking noise happen 3 times before the blower shut off. I did not however smell any LP Gas. So, it seems it's just not getting any gas to light the flame?? I also noticed a small piece of a mud-dobber nest in the intake and was able to remove that, but it made no difference. Also, just FYI...the unit is made by Suburban.
There may be more mud daubers up inside which can cause problems, I believe you must disassemble in order to clean out the heat exchanger. This is not the first time I have heard about this in the last few weeks and it has convinced me to order the screen kit.
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Old 12-14-2022, 05:49 PM   #9
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But before going to the trauma of removing and tearing things donw, I like to look for easy ways to test before deciding if the sail switch is the real problem.
Some thought on the sail switch shows it is a microswitch that closes when the air flow is good enough. Two things are obvious. One failure can be the switch is bad and needs replaced but the more common one is that it is just not getting the air flow to move and that can be tested pretty easy. But that "easy" depends on which furnace and how easy to get to that switch.

That's where the manual or even the Winnebago parts drawings can help. Depending totally on the drawings can have some downside if they happen to have changed furnace model in mid year, so that things don't match what you have???

https://catalog3d.winnebagoind.com/menu/Parts.htm
Click these snips to get a better view of things.

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Two things the drawings can do for us. It can help spot the switch and where it sets and also how the air flows over, around and through the furnace.
There is one motor with two shafts holding two blower fans.
I marked in blue the way these line up on the motor shaft.

I've marked cool air going into the combustion chamber as green and it becomes hot as red and comes out the vent.

See item 44 that lists as being the microswitch? If it has to close to make the pocess move on to open the gas valve, one way to make that appear to happen is to tie the two wires in and out of the switch, together with a temporary jumper wire. I like a pair of alligator clips on a small wire. If those two wires are connected together, it is the same as the switch contacts closing and things should then move ahead with the gas valve opening!

That brings us to item 26, the gas valve. It will be bulge in the gas line with two wires going in and out. Prettyeasy to spot in many cases. One way to test it is to just have a hand on it and feel or hear it click or move when it should.
With a meter, you can look for 12 volts to show on those wires at the right time as it comes from the board.
There are odd times when that valve may be getting the power from the board but it simply sticks, so it's worth just whacking it with something like a screwdriver to see if it pops loose!
If you are getting the sail switch closed but no voltage going to the gas valve, begin to suspect a bad board or bad connections!!

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Old 12-15-2022, 08:36 AM   #10
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Yep, you were right about no voltage getting to the gas valve. I appreciate the detail you provided in your post, Richard! I called a mobile rv tech and they had a board in stock and were able to replace it in about 20 minutes. All works well now, but they did find a leak in the propane valve and didn't have the knowledge to repair that. If you have any suggestions there, please let me know. I called a propane company and they said they don't work on RVs, which confuses me because propane is propane...but anyway??
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Old 12-15-2022, 11:10 AM   #11
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That's often the problem! We can make progress but it may cost us! But I've heard we can't take it with us, right?

For the gas leak, I assume it is at the furnace gas valve, not the valve at the tank?
If true, it depends on exactly where the leak is found. There is a copper gas line comes into the furnace with a flair nut to meet a flair fitting on the valve. One place to find a leak is when those two fittings are not tight, so that gas can come out where they should meet really tight. Maybe just loose and a couple wrenches to hold one while turning the other?
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OR it can be a case where somebody has tightened them way past good and it can totally crush the end of the soft copper pipe so far it leaks. Sometimes there is enough extra line to cut the end off and make a new flair?

Or is it just some place in the valve body which may have cracked?

Devil is in the details but if needing a new valve, that may lead to going to online or Suburban dealers for a new valve. Check to make sure WHICH furnace before buying as I would assume there are different size/type valves?
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Old 12-19-2022, 08:05 PM   #12
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The leak must be in the valve after being activated. If it were upstream your tank would run out. I believe.
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Old 12-21-2022, 08:34 AM   #13
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But that isn't clear and may be happening!
Would most of us notice the tank going dry a bit quicker than normal if we are only random users whose use varies so much?

But then the real way to look at a leak is so simple that many miss it. A soap bubble check will turn up most leaks if we mix the soap right so that it will cling to things long enough for even a small leak to show.
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