A/C venting

[MAMalody]

I have a 3790RD and with this 117 degree heat am having some cooling problems. Since the a/c in my bedroom seems to keep cool, what would happen if I plugged the vents into the bedroom from the den A/C and would force that air into the rest of the 5er. Is that problem? Would it cause any problems?

[Theunz]

Someone a while back wrote that after studying the installation manual for their a/c unit they determined that Montana wasn’t putting in enough outlet vents to handle the airflow. They added, if I remember correctly, 2 extra vents and saw an improvement in cooling. That being said, it would seem that closing off any vents would be detrimental to your cooling.

[Kyle and Lisa]

We have the same rig. I find it best to start running the a/c at 70 degree's early in the morning before it gets too hot and put the awning out ASAP. Also try turning your vents in different directions until you find what works for you.

[DutchmenSport]

What you are saying is, both air conditioners are connected together to your ductwork in the ceiling. When running both AC's at the same time, the bedroom cools just fine (of course, it's a much smaller room). The main living area does not cool as much. (of course, it's a much bigger space).

I would not attempt to block anything in the air ducts to separate the two. Instead, place a fan facing out from the bed room to help circulate the cooler bedroom air trapped in the small space.

Another well placed fan in your kitchen area facing toward the back of the camper (toward the living room), will help tremendously also.

Ours is a front living room and the bedroom is in the rear. We do have a ceiling fan, and when the ceiling fan is on, the temperatures between upper level living room, bottom level kitchen (open to each other), and bed room are pretty consistent. However, if the bathroom door is completely closed, it will be freezing cold in there. We have to leave the bathroom door open to circulate the air, otherwise sitting on the toilet is like sitting on an ice cube. Also, when we run heat, the bathroom turns into a sauna. We have to leave the door open also.

Get fan. They will help a lot.

[DQDick]

What I have done in both my rigs is cut out every other rib in the supply vents in the rooms I want more air to go to. Also, while you're up there trim the mounting so that it doesn't protude into the duct work it'self.

[MAMalody]

Hmmmm. Thanks all for the input. If I ever get it figured out I will let you know.

[AZ Traveler]

Michael,

You are getting to 3 a/c country once it gets to 117. With 2 a/c a typical split between inside and outside temps is 25 deg or so.

[wjg315]

I just recently took Dicks advise and cut every other rib out of the vents. It made a huge difference in our rig. You can definitely feel the air coming out of the vents now. We also covered the return vent under the stairs and covered the floor furnace vents.

[L0veless]

just a thought when you were working on the intake did you notice how large the space between ceiling and roof? there are a bunch of write ups about the duct work collapsing and restricting the air flow. we never noticed this until a hot day and started to look, sure enough our living room duct had collapsed to about an 1". placed 2 I believe 1-1/4 dia. pvc tubes 10 inches long to open up and keep open. HUGE improvement.

[ShaneGreen]

Keep in mind that with the cold air return under the stairs open you are also cooling off the basement....holding tanks, storage and all. The first time I opened my basement and it was cooler than my bedroom I figured it was time to take action. Like someone above posted, cover those up.



If you're not sure about cutting out every-other fin in your vents, just pop them out of the ceiling for a few hours and you'll notice a major difference. I bought a closable vent for the bathroom since it was always so cold in there. It doesn't seal off tight, so the room still gets cooled without being an icebox.


The skylights are also a huge source of heat. We put reflectix in the kitchen one and one of those stained glass looking designs from Home Depot in the other.

[bshgto]

Have this problem to and have tried or modified all the usual fixes with minimal improvement. What I did do was but a 5000 btu a/c in the bedroom window and a 5000 btu a/c in the living room window to see if that help . Yes it did with the addition of 10,000 btu`s it kept the unit cool all day in the blazing sun. So maybe the 3rd a/c with the control box disabled to run all 3 buttttt..... considering the kitchen one will have to be a dump unit you will have another a/c that sounds like an SR71 in full after burner while trying to watch TV or just talk
So the fix is a mini Spilt A/C system super quit, another 12,000 btu`s, is a heat pump that works down to 12 degrees (big plus) not to hard to install with enough motivation, less than 1,000 dollars. But where to put the outside unit? It is small and the back of a 3791 has more space than you really need, put it on a slide out tray to fit , flexible refridg. lines form the A/C supplier. I might try this cause I don`t want the noise. This is a non standard approach to the problem but I think the time has come for this. To be continued...........

[skippydoo]

We are in the Carolinas, HOT hot hot and humid is our way of life.

Thank God for our dump ac in the bedroom it's great. The air flow in rest of rig was not enough to cool our unit. My husband had to get UP in the vents, push a lot of stuff out of the way and re tape. He also built cones to force the air downward in the two vents located as you first walk in the rig.

MADE a big difference. Now our rig is freezing--we keep it very cold.

We covered the sky lights with those foil things (not pretty but who care) and we also have foil shields at all the windows in the main cabin. Thank God those windows are kinda tinted so no one can see them.

Our rig is 39ft--He searched on youtube and found a lot of help with what to do and how.
Good Luck..WE would have sold it IF my husband was unable to fix the problems the builder should have done in the first place. This should not be a huge problem with their rigs.

[2 Yoopers]

I sold my Montana and went back to a dp. because it suits us better. Loved everything about our Montana except the air conditioning. I did all the mods to the collapsed duct work, replaced the vents with high flow units. I even added two new vents in the kitchen area. I did see improvements good enough for me in upper Michigan, but I could not imagine using it in a warm climate.
Anyway my dp has 16 of the high flow vents where I believe the Montana had 8 restrictive vents. I have Dometic air conditioners 3- 15k units. We use 2 units to keep us 70 degrees in 91 degree heat today. I believe that Montana did not install enough vents, based on a 43 foot motorhome having twice as many as a 41 foot fifth wheel.

[GreG L.]

We did a few things for our two AC rig. We cut the ribs in the supply, put white covers over both roof vents and blocked off the bathroom and storage vents, this made a big difference, at 105° outside it's nice and cool inside. The bedroom is still much cooler than the living area and I don't think blocking one or more of the vents would push more air to the back (vents are most likely maxed now). I like the idea of putting more vents in the living area, has anyone done this?

[VagabondLove]

I added additional intakes… https://www.montanaowners.com/forums...ad.php?t=83870

It works great now!

[Kirch1]

New Member

Join Date: Aug 2021
Location: Afton
Posts: 2
M.O.C. #29387
I just purchased a 2021 Montana high country. After looking into it I’m beginning to think it is a Montana trait as a pertains to the air-conditioning. What you described as it pertains to cooling the front and the main cabin is exactly what is happening with this brand new camper. I have owned six other brands of fifth wheels all of them 40+ feet long and I’ve never had an issue with cooling down the unit. Ever. And I use and live in the same conditions. Not until I bought this new Montana has it been an issue. The dealership I bought it from basically told me this is an ongoing issue with Montana and has been. Their suggestion and solution is for me to put a third air conditioner in the unit. Now, this is not the only issue with this camper so I do not know how long I will keep it. But, if I do keep it then I will be putting in third one in the unit so I stop fighting with it.

[HondoSwatdog]

Did you ever figure it out? I have a 2021 3780RL and I can't get the temp down in this heat. I had to bring in a portable 3rd A/C unit. Any help would be appreciated.