collapsed a/c return ducts

[joe direnzi]

Fourth month of camping in our 2018 3721rl.Everything going great ,knock wood.Two nights ago, the fwd a/c started cycling off.Fan running ,compressor off.I have read different treads about collapsed return ducts.Took grills off and found the ducts were collapsed.Is there a previous tread that explains what size pvc pipe to use and what length and type?Btw a/c discharge temp.36 degrees.Believe a/c freezing up with restricted air flow.Thank you all

[CarWin]

If memory serves correctly, it should be 1&1/2" pic pipe, about 2' long, just regular white pvc piping.

[joe direnzi]

By chance ,do you remember how many pieces?Thank you for the help

[DQDick]

I put a 9" piece of 1 1/2" PVC pipe on each side of the vent, so I used 8 for the four vents in the rig.

[Texan]

I installed a 10'' 1 1/4'' pvc in each return air vent . Works great.

[Golfmedik]

Yes they are 1.25" pipe as the outside diameter will be the 1.5" and cut them to 9" in length and take off the sharp edges made due to cutting them. Place them on each side of the return.

[Baldicon]

Originally Posted by joe direnzi

Fourth month of camping in our 2018 3721rl.Everything going great ,knock wood.Two nights ago, the fwd a/c started cycling off.Fan running ,compressor off.I have read different treads about collapsed return ducts.Took grills off and found the ducts were collapsed.Is there a previous tread that explains what size pvc pipe to use and what length and type?Btw a/c discharge temp.36 degrees.Believe a/c freezing up with restricted air flow.Thank you all

Joe, are you sure the fan is running and the compressor off? I'm having the opposite problem. The fan is cycling off/on but the compressor continues to run. The fan will run for maybe 30 seconds and then shut off for 2 or 3 seconds and then run for 30 seconds again. Repeat. Repeat. And then eventually, both shut off. I think I have good air flow and the trailer is staying cool.

[mtlakejim]

Hey guys. We are camping in the southern heat so this is a major issue for us. There are two, what appear to be the return air vents on either side of the front AC. When I remove the grills it appears to be something like corplast that makes what I think is return air ducts about a foot wide and inch tall??? Is that correct and is that what y’all are sticking the pvc pipe in to prop it open?? Considering the layout do you put crossbars in to keep pvc properly oriented?

[Texan]

I installed 1- 10''- 1/14'' diameter pvc in each duct. I removed the register and stuck pipe inside length wise of the register then turned the pipe toward the center of the room and pushed the pipe in flush with register or beyond keeping the pipe in center of the duct. Some use 2 pipes in each register with one on each side but one seems to suffice as long as you install pipe in center of duct as the center seems to be what sags.Like golfmedic said take the rough edges off of pipe that has been cut. Also scoop out with your hand the sawdust just inside the register then vacuum out the rest.

[cghsatx]

Originally Posted by Texan

I installed 1- 10''- 1/14'' diameter pvc in each duct. I removed the register and stuck pipe inside length wise of the register then turned the pipe toward the center of the room and pushed the pipe in flush with register or beyond keeping the pipe in center of the duct. Some use 2 pipes in each register with one on each side but one seems to suffice as long as you install pipe in center of duct as the center seems to be what sags.Like golfmedic said take the rough edges off of pipe that has been cut. Also scoop out with your hand the sawdust just inside the register then vacuum out the rest.

Anyone know how these ducts are put together? I did the PVC treatment on my 2019 3731(it had all the commonly reported AC issues) last weekend but was a little concerned if the PVC would put too much pressure on the duct. If its just taped together pieces of Styrofoam, it might split. It was easy to slide in the PVC and it did open up the space quite a bit, but I have no idea how long the return air duct is and maybe does it collapse down again past the end of the PVC?

[Mikendebbie]

There are several "Keystone Montana Factory Tour" videos on youtube.
At times in each video you can see the ducts.
I like the "Home with the Hoopers" video here...ducts can be seen at ~10:00 mark.

https://www.youtube.com/watch?v=o0W2PeLlUBY

I took some screen shots from a couple of videos that you can look at below.
The first screen shot is from "Home with the Hoopers" video and it does indeed look like a styrofoam box. I have never touched the interior of mine...seems like if it was styrofoam you could see it! In the second pic you can see a joint taped together with aluminum HVAC tape. Pay attention to the dates of the youtube videos because duct material may have changed over the years.

[John Sigmone]

My 2 ducts are definitely collapsed. Can someone please tell me the length from the return to the end of the duct? And is it a straight line to the AC UNIT?

[Mikendebbie]

The ducts are like a racetrack running full length of your rig like the screen shots show above. I doubt your ducts are 100% collapsed…for example from point A to point B in the screen shot below. They may be collapsed at a few points where registers were cut in. The idea of sticking some little pieces of PVC maybe 6” to 12” into the collapsed opening is to prop open and support the collapsed top side. I drew a bad sketch on the screen shot below.

[mtlakejim]

Sounds like what I need to do ASAP! Currently the rear air that has the return directly under AC cools blows and cools far better than front AC with its ducted returns. So fairly sure that is issue. Easy fix but I realllllllyyyyyy wonder about the engineer who thought the ducted returns were a good idea!! What were they thinking???

[kench]

Originally Posted by mtlakejim

Sounds like what I need to do ASAP! Currently the rear air that has the return directly under AC cools blows and cools far better than front AC with its ducted returns. So fairly sure that is issue. Easy fix but I realllllllyyyyyy wonder about the engineer who thought the ducted returns were a good idea!! What were they thinking???

Probably along the lines of Hey Guys I can save us about 5 bucks if we change to this style. May upset the consumers but 5 bucks is 5 bucks.We have a 2016 3790RD with elevated rear den a/c was terrible but the 59 F cool air could not get into the living area. Had 2 a/c vents in living room 2 in bedroom and 4 in kitchen area. I cut 2 more in the living room and 2 more in bedroom. I replaced all of the outlets with adjustable and closeable style . Replaced all 13 outlets with Spaceport 8840wh at about 8 bucks each from Amazon. Most of the outlets had collapsed in the off door duct so had to stick pieces of 1 x 2 pine to hold them open. Makes a HUGE difference.

[2 Yoopers]

After reading a lot of the posts here I checked the return air ducts on my 2015 3711fl. I found them collapsed and the openings cut way smaller than the vent. I used a Dremel with a carbide endmill and trimmed the openings bigger, then taped with aluminum tape. Added the pvc in the center to open the ducts back up. I found new outlets at Dwinc on the web, model is 8850 and they are larger than the original outlets, adjustable, closeable and flow 20sq. inches of air, compared to the stock 12sq. inch ones. Used dremel tool to open hole to 5 7/8” then taped the gaps up between duct and ceiling. New outlets are 7/8 tall instead of sticking way up in the ducting. Replaced 4 in the front living area, 2 in the bedroom, 1 in the bathroom and added 2 in the kitchen where there were none. This worked great, very pleased with the cooling now.

[mtlakejim]

Originally Posted by 2 Yoopers

After reading a lot of the posts here I checked the return air ducts on my 2015 3711fl. I found them collapsed and the openings cut way smaller than the vent. I used a Dremel with a carbide endmill and trimmed the openings bigger, then taped with aluminum tape. Added the pvc in the center to open the ducts back up. I found new outlets at Dwinc on the web, model is 8850 and they are larger than the original outlets, adjustable, closeable and flow 20sq. inches of air, compared to the stock 12sq. inch ones. Used dremel tool to open hole to 5 7/8” then taped the gaps up between duct and ceiling. New outlets are 7/8 tall instead of sticking way up in the ducting. Replaced 4 in the front living area, 2 in the bedroom, 1 in the bathroom and added 2 in the kitchen where there were none. This worked great, very pleased with the cooling now.

I could not find a dwinc brand of vent on the web. Can you verify the brand please.

[2 Yoopers]

Yes, it is Dwincorp.com. They handle quite a few of the outlets and other rv parts. I paid 6.00 for each outlet, includes the collar that screws into the ceiling and the snap in adjustable louver that covers the screws. Shipping was fast as well.

[Mudchief]

On our unit it was only the center sucking together so i just put 1 pcv in the center of each vent.

[Baldicon]

What initially made you think the ductwork was collapsed? Not cooling? Couldn't feel are coming out of the supply registers? My unit has a 90 degree hard plastic ell that transitions from the return register to the ductwork which is maybe 1" tall. I can feel are coming from my supply registers and the trailer is staying cool. But my fan cycles on/off while the compressor continues to run until the thermostat is satisfied. I don't think a collapsed ductwork will cause this, but not sure. I have a inspection scope somewhere in my cluttered garage (home) and will take a look my ductwork when I find it. Every thing I have is somewhere.