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.

[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???

[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.

[Golfmedik]

Several of us working through our units not cooling stumbled across the return air ducts had collapsed. When we put 1.25" PVC pipe(outside diameter of 1.25 pipe will be 1.5") to open the ducts back up to spec, the units started cooling much better. The more air the unit can get, the more it puts out. Plus, it keeps the unit from freezing up. Most of us have been told to run the AC units on HI all of the time as in higher humidity situations and running on LO, the units will short cycle and freeze up.

[DadsHemi]

I just installed 3 pieces of 1” couplers which are 1-1/4” OD in all 4 of my return ducts. I put one in the center and 2 on each side about 2” away from the sides. Made a huge difference.

[ingalmi]

A/C cycling, return ducts need to be free of restriction so check this first.
Next;
Pretty normal if operating in auto fan. Bedroom unit if it’s the front one will cycle more because of cooling room area. I use high fan on both until just before ready for bed then switch to low fan. Just personal preference. Here’s what some don’t know about, remove the thermostats off the wall (2 screws) and you’ll find a huge hole where they pass a small wire through. Guess what the thermostat is really reacting to? The inside of an uninsulated wall! Use tape or insulation to cover/plug the hole allowing enough room for the wire. Will make a difference in how the system works. Good luck and happy camping

[Baldicon]

My return ductwork appears to have a spacer in the middle which I assume is there to prevent collapse. Keystone was supposed to upgrade the ductwork Fall 2017. Does the pre-Fall 2017 ductwork include this spacer? I tried to attach a picture, but don't know if I did this correct. Surely the web master can come up with an easier way to attach pictures.

[DQDick]

My 2017, built in February, doesn't have the plastic on the end of the return air that they added in the fall of 2017 and on. Would be interested to know if these actually solved the problem.

[Phil P]

Hi

I am having some problem here understanding this thread.

Our 2009 Montana has a return air duct at each AC that is about 8 inches long and 4 inches wide (estimate I haven’t measured) and that is all for return air.

It has several distributions ducts the supply cool air to the trailer when the main cold air vent is closed.

Has Keystone changed this?

Phil P

[DQDick]

Consider yourself lucky. Yes they have changed. After enduring complaints about the noise the older units like yours makes they came up with the Whisper Quite system. The return air on those units is near the sides of the ceiling and then it is ducted back to the unit. Dometic came up with the unit, but the real problem comes in how the manufacturers are installing them and Keystone isn't alone in that.

[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.