Air Conditioner Duct Upgrades

[Foldbak]

Ok lets talk about the lack of air flow coming out of the ducted vents and these stupid new blade air vents and the blade pure airflow system. It hit 100 in Sacramento recently and it was 91 in the trailer. I did an experiment by turning on both AC units. (which to my surprise both worked on a 30 amp circuit). I didn't run both of them very long. Anyway I let the rear AC run for a couple hours and inspected the trailer expecting to find it to be in the high 70's only to find it at 88. I got on a step stool and checked the airflow. It is awful. Better flow after removing the blade air vent covers. Then I started doing some research and found the the ducting at the plenum is rarely sealed properly. But the fixes I see online are pre this.



https://www.keystonerv.com/innovatio...ean-quiet-cool


Before I go tearing crap up I thought I'd ask if anyone has tried to tackle this newer air system....

[RMcNeal]

I do not have that new system, but one thing I did to ours that did make a very strong difference was this. I went to each vent and removed the diverter. I should pop off fairly easily. I put small pieces of PVC pipe in the vent inside to prevent the racetrack duct from collapsing. Then I used silver HVAC tape around the plastic vent insert to seal it from allowing any air to escape into the attic. On a few, I found that the plastic insert was protruding up into the vent as much as an inch past the styrofoam insulation. In those cases, I cut the vent down with a razor knife to be flush with the duct work before taping it. Did the same to each return vent.
I found that the air flow increased dramatically on most of the vents, some more than others.
Got the idea from Gordon Hallof, a fellow Marine of course. He did a really detailed write up on his work on this. See his post here...
https://www.montanaowners.com/forums...highlight=duct

[1retired06]

Originally Posted by RMcNeal

I do not have that new system, but one thing I did to ours that did make a very strong difference was this. I went to each vent and removed the diverter. I should pop off fairly easily. I put small pieces of PVC pipe in the vent inside to prevent the racetrack duct from collapsing. Then I used silver HVAC tape around the plastic vent insert to seal it from allowing any air to escape into the attic. On a few, I found that the plastic insert was protruding up into the vent as much as an inch past the styrofoam insulation. In those cases, I cut the vent down with a razor knife to be flush with the duct work before taping it. Did the same to each return vent.
I found that the air flow increased dramatically on most of the vents, some more than others.
Got the idea from Gordon Hallof, a fellow Marine of course. He did a really detailed write up on his work on this. See his post here...
https://www.montanaowners.com/forums...highlight=duct

I did basically the same thing. It helps a lot!

[jsb5717]

If you have the new Coleman system then I’m not familiar with that one. However, there are some basic, universal things to check. You got a good list above. I did the same thing in pulling every vent cover off to check the connection to the ducting itself. The top of the vent should be flush to the inside of the duct. If not then it should be trimmed. The aluminum tape is a good idea to make sure there is a good seal around the vent at the duct so there is no air escaping into the attic space. You can also run a boroscope through your duct system just to make sure it’s all open.

On ours the boroscope showed the ducts to be nicely open. But we still had marginal air flow and a warm trailer in 100 degree weather. However, at that time we only had one air conditioner. Now with 2 AC’s we have been in 95-100 degree weather for a week and with both AC’s running we have been very comfy. So, IMHO, 2 AC’s running is a must in 90+ temps. I installed EasyStarts in both units to make sure I could run them on 30amps if necessary.

Edit: Another thing we learned is to keep the window shades closed on the sunny side of the trailer. We also close the shade in our kitchen skylight. The trailer’s darker but cooler. It’s amazing how much heat gain you get through the windows.

[Foldbak]

That's a lot of good info. I'm going to start with removing the intakes and see what the plenum connections look like.

[jsb5717]

Another thing to check: In the heat of the day see if you feel hot air blowing in from the return vents under your steps. We had a lot. I’ve since sealed every opening to the basement area, where the furnace is located, including the holes in the floor to the underbelly and the gaps above the separation wall at the upstairs floor joists. Now the only air movement has to be from the trailer itself. It dramatically cut down on unwanted hot air movement in hot weather.

[Foldbak]

Originally Posted by jsb5717

Another thing to check: In the heat of the day see if you feel hot air blowing in from the return vents under your steps. We had a lot. I’ve since sealed every opening to the basement area, where the furnace is located, including the holes in the floor to the underbelly and the gaps above the separation wall at the upstairs floor joists. Now the only air movement has to be from the trailer itself. It dramatically cut down on unwanted hot air movement in hot weather.

I dont completely understand the step vent. What has that got to do with the AC system. I thought it was just for the forced gas heat.

[jsb5717]

Originally Posted by Foldbak

I dont completely understand the step vent. What has that got to do with the AC system. I thought it was just for the forced gas heat.

It’s not directly related to the AC, but it has a lot (or it did with us) to do with heat build up in the trailer. I found that hot air was somehow being forced in, or sucked in, to our trailer through the return vents. When I investigated I found that behind the basement storage wall, where the furnace is located, that there were a lot of different openings to that space. Somehow, ambient hot air was coming into that space and ending up in our trailer in the heat of the day. I plugged everything with rigid and spray foam so that the only access to the furnace space was through the return vents. That has cut down on a ton of unwanted heat coming into our trailer.

I can’t really explain in from a thermal dynamics perspective. I just know, from experience, that I needed to do something to keep that outside hot air out of our rig. I think I succeeded. I also think it reduced demand on AC performance.

[dieselguy]

Foldbak ... The youngest Montana that I've been in behind the rear wall in the pass thru storage area is a 2019, but I'd guess newer ones are very similar. The area behind the steps at the junction of the drop frame and upper frame is really all one big area connected directly to the underbelly. This link will show more so what I'm trying to describe. https://www.montanaowners.com/forums...ht=design+flaw
On windy days until I did all my mods, you could feel warm air puffing into the living area right out the stair vents which "are not connected via any duct work to your furnace".

PS Like said, plug up any openings in your underbelly as well.

[DavidG425]

We had a similar problem, so one day when a technician came out about a different issue, I asked him about it. He explained that the southern CA sun was heating up the roof, which then heated up the styrofoam insulation that the air ducts are cut into. Until the AC's could cool down the styrofoam, we wouldn't get much cold air out of the vents.

That's when I started looking for something to put on the roof. We had a neighbor that had one of these. I ended up getting one and it made a HUGE difference!!!

With all 3 AC's running, I could keep the inside temperature 25-30 degrees cooler than it was outside when it got over 100. Less than 100 outside, the bedroom AC would cycle off and on to keep it around 72. The AC in the middle would run most of the day to keep it less than 74, with the rear AC helping out some too.

[Brian S]

What did he put on the roof?

[Carl n Susan]

Originally Posted by Brian S

What did he put on the roof?

Click on the underlined "these" in the above Post.

[VagabondLove]

We ended up adding two additional intake vents to allow more air into the system. Improvement found here https://www.montanaowners.com/forums...ad.php?t=83870

[ShaneGreen]

When you have the air vents down, cut out two of the louvers. I did one on each end. Then pop the vent back in and feel the difference between it an unmodified vent. Big difference in air flow. Those louvers real cut down the speed and volume. I modified all of ours.


If you're sitting in place for more than a few days, I also made solar sun shades for the windows. Massive difference in the internal temperature. Folks have been making these for years, but when I was reading up on them a lot of the images were missing or info was outdated, so I documented my build. Here's a write up I did: https://www.wanderandreflect.com/202...creens-for-rv/

[Route66Rambler]

Shane, why did you use velcro instead of magnets like the MagnaShades?

[ShaneGreen]

Route66Rambler. . .I had planned on using magnets, even bought some, until I read someones post about using them. He was attaching some store bought shades (not sure if they were MangaShades) to a side window of his motorhome and the pull of the neodymium magnets was stronger than the grip he had on his shade. . .the two magnets coming together had the same affect as a lawnmower throwing a rock.



I believe one of the magnets in the MagnaShade is encased in fabric, which would lessen the impact. But that's not really practical in this type of screening. Windshield glass is also a lot thicker and heavier duty then what is used in these 5th wheel windows.


Knowing my ability to break things in new and interesting ways, I figured velcro was a much safer bet. Someone also questioned the heat transfer in those concentrated areas when using magnets. So I went the route that offered the fewest possible issues.

[jayernst]

Has anyone tried the air duct modifications what is in this video?

https://www.youtube.com/watch?v=fBAUuMoD-ec&t=166s

[VagabondLove]

I don’t have that type of unit in my Montana. But, it looks like it could be an improvement.

[Hblick48]

Originally Posted by jayernst

Has anyone tried the air duct modifications what is in this video?

I did this upgrade. Made a huge difference in airflow out of the a/c vents. Also, unit is much quieter.

[PND Mountaineer]

Yes, I have modified my AC unit with a kit I got on line. Not sure if I am allowed to use the company name. Also got rid the that junk Dometic three wire thermostat and control box. I can give you deals if you want by sending me an email.
Pat M.