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Old 09-09-2020, 11:14 AM   #1
webbhead64
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No furnace air movement to 2 vents - 3761FL

Hello:

I'm new to the group, and a new Montana owner. Just picked up a 2020 3761FL a week ago. I've already leaned quite a bit in this forum.

Last weekend was our maiden voyage, and it got cold enough to have to fire up the furnace. During our PDI we checked the furnace functioned, but shame on me for not checking air movement to all vents.

So here's the deal on the vents in the various locations.

1) Middle of Front Living area - Good air flow
2) Vent on forward side of kitchen island - nearly no flow at all. It is probably the closes vent to the furnace, too.
3) Vent on rear side of kitchen island - GREAT air flow
4) Vent on floor of 1/2 bath off kitchen - GREAT air flow - actually, i believe it is connected to the kitchen vent mentioned in #3, above
5) Vent in main batch in rear bedroom - Nearly no flow at all
6) Vent in rear bedroom floor - Nearly no flow at all. I believe that #5/#6 are connected together via under floor duct work.

So, being new to a 5th wheel (Have had many travel trailers previous), I'm not sure what the likely cause would be. Take the vents in the rear bed/bath, for example. When I look in the basement under that room, I just see a piece fairly short piece of sheet metal between the floor joists, which I believe is connecting the 2 together. I don't see where duct connects into it from the furnace, so not even sure how to trace it back to the furnace.

I've also not opened the wall from the pass thru compartment to access the furnace. That's my project for this weekend.

I'm trying to avoid taking it in for service, as we have 4-5 more weekends of camping booked, and I know it will sit at the dealer for a couple of weeks if i take it back right now.

So, why am I posting when I haven't done much troubleshooting on my own yet? Well, I'm really looking for the likely culprit on this lack of air flow. Disconnected ductwork, blockage, something else? Looking for ideas of where to "start", figuring many of you have probably encountered the same thing, possibly with the same model. Also, how do I deal with the fact that I don't even see a clear path from furnace to the back bedroom/bathroom?

Appreciate any help or guidance you can provide, as I prepare to dive in and figure this out.
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Old 09-09-2020, 12:15 PM   #2
DQDick
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When you open the basement wall, behind the furnace you will probably find a plenum with connections going to the various ducts. I would be surprised if one or more of the connections haven't come loose. Several folks have had that problem.
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Old 09-09-2020, 12:20 PM   #3
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When you open the basement wall, behind the furnace you will probably find a plenum with connections going to the various ducts. I would be surprised if one or more of the connections haven't come loose. Several folks have had that problem.
Yep, this is likely the problem. I had this issue with all 3 new Montana fivers I bought.
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Old 09-09-2020, 12:35 PM   #4
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Originally Posted by DQDick View Post
When you open the basement wall, behind the furnace you will probably find a plenum with connections going to the various ducts. I would be surprised if one or more of the connections haven't come loose. Several folks have had that problem.
I'm hoping it's that simple. I'll let you all know what I find after I get behind the wall, this weekend.
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Old 09-17-2020, 08:47 PM   #5
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When you open the basement wall, behind the furnace you will probably find a plenum with connections going to the various ducts. I would be surprised if one or more of the connections haven't come loose. Several folks have had that problem.
All were connected at the furnace. ☹️
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Old 09-17-2020, 09:06 PM   #6
Tom N OH
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The next most likely place is where the step up from the kitchen area to the bedroom area is. There’s probably a flexible foil duct to go from one level to the other. I’ve seen ducts pinched, torn & completely disconnected. I’m sure that there is a false wall in the rear basement that can be removed just like in the front.
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Old 09-18-2020, 06:45 AM   #7
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Our is an older model and we experienced a similar issue when it was new. Living room floor vent closest to furnace not much air other 5 vents were fine. Furnace was heating the unit just fine. Talked to service manager about it. His explanation, "There is a baffle, (actually just a bent piece of sheet metal in the main duct run), just ahead of vent 1. It pushes the majority of the air past the first vent to the remaining vents in that run. He said without it too much air goes to first register not leaving enough to adequately heat the rest of the main floor." Didn't make a lot of sense to me but with a flash light and a mirror I was able to see the baffle. I do seem to remember the three upstairs ducts were connected via two flexible tubes off the plenum. One direct to the bathroom vent and one into the pan duct supplying the upstairs bedroom. I did have to reattach the one flex duct to the bathroom register years into ownership.
It's heated fine for 15 years so I guess it working as designed. (and we have been in some cold climates over the years) If it is warming the unit OK, I wouldn't get hung up on the air flow. These things are not like a house heating system and are not very efficient but they do the job they are designed to do. Let us know your findings.
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Old 09-18-2020, 06:55 AM   #8
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Originally Posted by DQDick View Post
When you open the basement wall, behind the furnace you will probably find a plenum with connections going to the various ducts. I would be surprised if one or more of the connections haven't come loose. Several folks have had that problem.
I also agree with this assessment. When I removed the wall in my basement, I was very surprised what I found under there. I had a couple of those flexible duct hoses that had popped off the furnace, and I quickly discovered how the underbelly is "heated" ... um .... smaller lines coming from the furnace and just open on the end, blowing under the floor. No wonder the camper uses so much propane to heat the thing, probably 50% of the heat is blowing under the floor into that open space .... thus.... the winter package and good to zero degree temperatures ..... oh yes????

It's possible your air ducts are adjusted in a similar way, to keep the pipes from freezing in zero degree weather. Some sections UNDER the floor need more heat than others to prevent the lines from freezing, as in those locations the water lines and sewer lines and holding tanks are located. My guess. But you'll be SHOCKED how much heat goes under the floor.
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Old 09-18-2020, 07:02 AM   #9
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Quote:
Originally Posted by DutchmenSport View Post
I also agree with this assessment. When I removed the wall in my basement, I was very surprised what I found under there. I had a couple of those flexible duct hoses that had popped off the furnace, and I quickly discovered how the underbelly is "heated" ... um .... smaller lines coming from the furnace and just open on the end, blowing under the floor. No wonder the camper uses so much propane to heat the thing, probably 50% of the heat is blowing under the floor into that open space .... thus.... the winter package and good to zero degree temperatures ..... oh yes????
It probably is good to zero they just don't mention how much propane it takes to get there! Believe it or not, our salesman actually told us that. 10 degrees is the coldest night we have experienced. We weren't freezing when we woke up and the water from the tank still pumped. And oh yes, we started heading south.
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Old 09-18-2020, 04:32 PM   #10
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All were connected at the furnace. ☹️
Take out the vent grills and use a mirror to look down all ducts and see if there are any collapsed or blocked ducts.
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Old 09-20-2020, 03:58 AM   #11
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Originally Posted by Tom N OH View Post
The next most likely place is where the step up from the kitchen area to the bedroom area is. Thereís probably a flexible foil duct to go from one level to the other. Iíve seen ducts pinched, torn & completely disconnected. Iím sure that there is a false wall in the rear basement that can be removed just like in the front.
Ours had 2 lines found "severed"...repair by CW didnt improve flow much. I ended up removing about 10 feet of 'extra' hose and installing 4" rigid ductwork in its place. There was so much 'extra' hose balled up in the underbelly that it created a torturous path for air flow. We have adequate air flow now.
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Old 09-20-2020, 07:50 AM   #12
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Originally Posted by Denny and Angie Miller View Post
Ours had 2 lines found "severed"...repair by CW didnt improve flow much. I ended up removing about 10 feet of 'extra' hose and installing 4" rigid ductwork in its place. There was so much 'extra' hose balled up in the underbelly that it created a torturous path for air flow. We have adequate air flow now.
Did you end up having to take off the corollary underbelly to do all that?
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Old 09-20-2020, 01:47 PM   #13
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If you cover the vent that has the good airflow do the other vents have increased airflow?
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Old 09-21-2020, 12:36 PM   #14
Denny and Angie Miller
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Did you end up having to take off the corollary underbelly to do all that?
Yes I did. Not all the way though. Reluctantly I made a cut in the coroplast parallel to the axles, then removed the screws from street side and the rear, allowing the coroplast to hang down by the screws on the curb side. When I was done I reattached all the screws and then used black gorilla tape to seal the cut I made parallel to the axles. So far the tape has held very well.
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Old 09-21-2020, 12:42 PM   #15
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Yes I did. Not all the way though. Reluctantly I made a cut in the coroplast parallel to the axles, then removed the screws from street side and the rear, allowing the coroplast to hang down by the screws on the curb side. When I was done I reattached all the screws and then used black gorilla tape to seal the cut I made parallel to the axles. So far the tape has held very well.
I meant "coroplast" not "corallary". Dang phone! :-) Thanks for the reply, Denny and Angie!
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Old 09-30-2020, 05:34 PM   #16
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If you cover the vent that has the good airflow do the other vents have increased airflow?
Last weekend I covered all vents (front living, kitchen and 1/2 bath). Are flow MAY have increased a small bit, but barely enough to feel. Has to be a kinked of run somewhere under there.
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