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Old 11-16-2017, 10:19 AM   #1
John Shasky
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Question Air Conditioner return Duct

I am having a problem with the rear AC not performing as it shouldI have read many posts abut rear air conditioner problems and some regarding collapsed return ducts. I have a 2014 3402RL Montana. The return duct is in fact collapsed to about 38th inch. I have tried fixes to prop it open. Since the ceiling and roof is curved I have found nothing flexible enough to span the duct. i also don't want to block air in the process. Worried also about damaging the duct. Tried pvc pipe, golf balls to no avail. Any ideas? Maybe i need to cut a new vent hole in the center below the AC? Increased noise? Or could replace existing return air intake vent covers with larger ones? I have an extend warranty but hate to deal with the dealer who would charge for evaluation and tell me it is performing as designed. It is not!
 
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Old 11-16-2017, 11:25 AM   #2
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Have you considered using 3/4" or 1" flexible tubing? Should be able to get it at any Lowes, Home Depot, Ace, etc. It is normally clear and thin walled.
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Old 11-23-2017, 05:25 PM   #3
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We have a 2016 3791 that has compressor and fan cycling issues but that is another issue. One of the times we had it at the dealership they found the return ducts in the den, the main area of the coach, had collapsed. They took 1/4" plywood and cut strips about 1 1/8 wide and maybe 2' or so long. One for each return. He put them into the duct turned flat so they would flex and go all the way in. He placed them in the middle of the duct and once it was all the way into the duct he turned it up on its edge which forced the duct open. One other thing, he cut the strips on a curve to match the curve of the roof. He actually took a piece of cardboard and made a template which took several tries to get it just right. He would hold it up against the ceiling and kept trimming on it until it matched the ceiling. Then he used the template to mark and cut the plywood strips. He also used plyers or channellocks to grasp the strips to turn them onto their edge. Works great.
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Old 11-23-2017, 07:18 PM   #4
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Sounds like you have a dealer that doesn't mind thinking and doing outside of the box.
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Old 11-24-2017, 07:06 AM   #5
John Shasky
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Thanks for the ideas. Will try the plywood idea!
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Old 11-24-2017, 07:38 AM   #6
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Same problem with our 2018 353 RL. Dealer installed 2 more returns added two new discharge ports. They matched the factory ones. Also used 1 1/2 pvc pipe to open up return and discharge plenums. We measured the distance of pvc needed cut to length and used a cap when pushing into place then removed the cap so no flow blockage. Wood might snag the insulation.

Actually works like it should.
Good Luck
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Old 04-22-2018, 05:34 PM   #7
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Happy Camper,
How long was the pvc? Did you install parrellel with the duct or perpendicular? How was it installed?
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Old 04-22-2018, 08:10 PM   #8
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parrallel to ducts had to play with the lengths to make fit
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Old 04-22-2018, 09:24 PM   #9
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parrallel to ducts had to play with the lengths to make fit
Thank you. I have to get mine fixed before I leave in a week.
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Old 04-23-2018, 07:47 AM   #10
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After 2 trips to Camping world and several weeks later: They replaced AC which had a coolant leak, however they tweaked it during the install and it didn't work when i brought it home. They had to order another AC unit and double up the gasket seal under it. It now works but I need to do something about the duct collapsing. I am thinking about putting spacers in the duct (not sure what kind) and maybe even adding two more intake vents or increasing the size of the existing vents.
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Old 04-23-2018, 08:18 PM   #11
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parrallel to ducts had to play with the lengths to make fit
What is the manufacture date of you camper? Montana was supposed to start installing redesigned ductwork sometime last fall that is not supposed to collapse.
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Old 04-24-2018, 03:28 PM   #12
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Beginning with what manufacture date would Montana's have the newer non-collapsible air conditioner ducting and return air ducts?
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Old 04-24-2018, 03:39 PM   #13
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Beginning with what manufacture date would Montana's have the newer non-collapsible air conditioner ducting and return air ducts?
Not sure of exact date, but sometime fall 2017.
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Old 04-25-2018, 02:00 PM   #14
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ac return

I had a good service company repair mine took 4 tries but its working. they used 1 1/2 inch PVC about 2 inches long BUT they had to install it at the return air vent BOTH inside and in the AC unit. it forced the pipe to open all the way thru. they took pics through out the process and the iphone pics showed daylight at the end.
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Old 04-26-2018, 02:38 PM   #15
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Originally Posted by happy camper x2 View Post
Same problem with our 2018 353 RL. Dealer installed 2 more returns added two new discharge ports. They matched the factory ones. Also used 1 1/2 pvc pipe to open up return and discharge plenums. We measured the distance of pvc needed cut to length and used a cap when pushing into place then removed the cap so no flow blockage. Wood might snag the insulation.

Actually works like it should.
Good Luck
Do you have any pics you can share? Especially of the cap you used while installing the pvc?
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Old 04-30-2018, 09:48 AM   #16
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No pics, the techs used their camera and showed me the pics before NO light.
after strong daylight. Denny do you ever make it to Mark Twain Landing, we spend the summer their. SITE 27
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Old 04-30-2018, 07:02 PM   #17
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We stay at C.O.E Indian Creek campground several times a year...was just there last week
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Old 08-03-2019, 03:42 PM   #18
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2014 Montana 3402RL/August 2019 Update: Well We are sitting here at 2 PM in the afternoon in Cave Creek Phoenix area (113 degrees outside). with both front and rear Acs running it is now up to 87 in the living room. Meat thermometer in an outlet measured about 66 degrees. I had placed spacers in the return ducts as suggested a year ago. I also took the intake air grills off and have the paper framed filters screwed into the ceiling temporarily, I thought it was working better. Thinking about cutting larger holes i the duct and put larger filters on the openings..Maybe the AC units are freezing up. I often wonder with the fact the the the accents on the exterior including the AC covers are black that maybe it causes the units to overheat, I'm sure the everyone who has problems with their Dometic dual systems has reached a high frustration point. Short of ripping out some ceiling panels and working on the cut system I don't know what else to do!!! I am close to a decision to sell/dump it. Not a very comfortable rv during the Arizona summers!!!!!
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Old 08-03-2019, 03:50 PM   #19
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John, your last line is the correct one, 'not very comfortable...arizona summers.'

rule of thumb and answer for a home a/c: 'How much can an air conditioner drop the temperature in your home? Air conditioners are designed to lower the temperature of your home's air by about 20 degrees. So if the air in your home is 85 degrees, for example, your air conditioner can lower your air's temperature to about 65 degrees.'

87 degrees isn't bad if it is 113 degrees outside. In this situation it isn't dometic, it is the heat in arizonia.
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Old 08-03-2019, 04:05 PM   #20
John Shasky
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John, your last line is the correct one, 'not very comfortable...arizona summers.'

rule of thumb and answer for a home a/c: 'How much can an air conditioner drop the temperature in your home? Air conditioners are designed to lower the temperature of your home's air by about 20 degrees. So if the air in your home is 85 degrees, for example, your air conditioner can lower your air's temperature to about 65 degrees.'

87 degrees isn't bad if it is 113 degrees outside. In this situation it isn't dometic, it is the heat in arizonia.
Thanks Mazboy. I pretty much agree with you . I do think however that if I could find some way to prop the duct work open to 2 inches, insulate the ceiling better, Paint the AC roof units white, it might get us a little more efficiency. The design of the return air while quieting the LR unit a bit I think having an opening at least twice the size might help too.
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