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Old 09-25-2018, 06:03 PM   #1
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Air conditioning duct problem

Ok guys, need some ideas of where to start - I'm thinking I've got a ductwork issue with the front air conditioning unit. Think the ductwork itself is ok but need troubleshooting ideas.

If the rear unit is running, there is good airflow from all outlets. Even bif room is pretty good for as far as it has to travel. If the front unit them comes on, flow into the bedroom naturally increase as does all other vents but not in proportion to what it is with just the rear one running. It's better, but not great.

If only the front one is running, airflow is minimal. I'm suspecting I've got a problem with either the plenum or air intake or output in the front AC unit.

Does anyone happen to have a good picture of how that plenum SHOULD look like and be separated ? I'd like to know what it should be like when I take it all apart so that I know what to look for. I'm thinking the main ductwork is ok as the flow is good with the rear air running.

Any suggestions and ideas from my learned colleagues are welcomed and encouraged !!

Thanks in advance all !!
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Old 09-25-2018, 06:54 PM   #2
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Vaughn, mine is the same way. I believe the duct work is not of sufficient size to handle the volume of both running. If one or the other unit is running there's good, well at least some, air flow from all ducts, but like yours it doesn't seem to increase much, if any, with both running.
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Old 09-25-2018, 07:55 PM   #3
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We also have the same issues. We run one or the other but not at the same time. I have been considering and most likely will soon be going back to the old ways and just have our bedroom ac direct dump in that room and then let the front do its thing. We can control somewhat with fans but as soon as I get up and shut the bedroom door when Char is sleeping the room becomes an oven.
All the RV,s we have had over the years and this is by far the worst unit as the ac's goes. Never Again!!!!
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Old 09-25-2018, 11:28 PM   #4
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Your front and rear AC's are ducted together?
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Old 09-26-2018, 03:13 AM   #5
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Vaughan, do you follow the Montana Forum?? There have been numerous post there about AC issues and what they have found is the Return Ducts are semi-blocked with wires or the duct it's half crushed. They have been inserting sections of 1 1/2 PVC into the duct to hold it open with pretty good success.
Trying removing the return filter housing and stick you phone up into the opening an take some pics and see what it looks like.
Something cheap to check out.
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Old 09-26-2018, 03:29 PM   #6
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Your front and rear AC's are ducted together?
Danny, I think you and I have almost identical units. I understand that the previous units have both AC's ducted together. Ours are separate.

I have often wondered which way is better. My bedroom unit will freeze you out with no trouble while the unit in the main area works harder to keep the temps. Also the rear has further to travel so I assume that is why the amount of air coming out is less.
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Old 09-26-2018, 05:10 PM   #7
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Michelle - I think you may be onto something. I'll check that out later today or tomorrow.
As I had mentioned in the original post, I think the supply ductwork is ok since if either unit is running I do have flow into the bedroom and main areas. The difference in flow between the two units though is tremendous. I know the rear unit is closer to the outlets in the living area and further from the bedroom but if it is the one that is running the airflow isn't bad. If only the front unit is running, the overall airflow is probably half of what the rear unit will do.

That's the issue I'm chasing. Funny, in almost 6 years I've never thought that much about it. But then this is the first summer in 110 degree Arizona sun !! Overall the coach did pretty well but since we are staying here for another season I'm looking to improve.

Still would like to see a picture of what that pl num area in the AC units should look like if anyone has one.
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Old 09-27-2018, 04:54 AM   #8
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Originally Posted by xtasee View Post
Danny, I think you and I have almost identical units. I understand that the previous units have both AC's ducted together. Ours are separate.

I have often wondered which way is better. My bedroom unit will freeze you out with no trouble while the unit in the main area works harder to keep the temps. Also the rear has further to travel so I assume that is why the amount of air coming out is less.

Danny and Larry,


We have a unit that should be quite similar to yours. Our bedroom A/C, like yours, will freeze you out while the one in the living room struggles and can't keep up when we are set up in direct sun here in Arkansas. Our thought was that the bedroom unit is cooling a significantly smaller area than is the living room unit and therefore works much better. It turns out that both of our A/C units were actually starved for return air.
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Old 09-27-2018, 02:20 PM   #9
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Danny and Larry,


We have a unit that should be quite similar to yours. Our bedroom A/C, like yours, will freeze you out while the one in the living room struggles and can't keep up when we are set up in direct sun here in Arkansas. Our thought was that the bedroom unit is cooling a significantly smaller area than is the living room unit and therefore works much better. It turns out that both of our A/C units were actually starved for return air.
That's good to know. What did you find and what was the fix?
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Old 09-28-2018, 01:04 AM   #10
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Wanted to thank Michelle. Stuck camer up into the returns for the forward air unit and it looks like partial duct collapse on the one side. I think my easiest way out is to add two more returns to each AC unit. Looking at it, it shouldn't be too hard a job as long as my hole cutting is accurate. ��
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Old 09-28-2018, 07:25 PM   #11
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I have been doing some floor duct maintainance and am noticing foil tape at some seams is letting go have been retaping on a as needed basis

Also noticing some return air leaks too but it's in the ceiling living areas drawing air around light cutouts too can tell by dust on old lights when I put led s in.

Leaks r opening up with age and heat from sun.
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Old 09-29-2018, 02:32 AM   #12
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Best tool for adding additional return ducts is an oscilating tool with a fine tooth half-round saw attachment.
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Old 10-02-2018, 05:15 PM   #13
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To check my ducts and other hard to see places, I bought an endoscope on Amazon. Couple this with a cell phone and a snake, you can see most anywhere. They can be cleaned with hot water and alcohol, so you can even send it down the toilet to find a blockage.
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Old 10-02-2018, 10:10 PM   #14
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Quote:
Originally Posted by Elliott & Vicky View Post
To check my ducts and other hard to see places, I bought an endoscope on Amazon. Couple this with a cell phone and a snake, you can see most anywhere. They can be cleaned with hot water and alcohol, so you can even send it down the toilet to find a blockage.
I have the same scope also comes on very handy. Very cheap to purchase as well
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Old 10-04-2018, 03:20 AM   #15
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We found that the A/C return air intake is located on one side of a truss and the return air duct is on the other side of the truss. They cut slots thru the truss so the unit could breathe but they are way too small. Widening them is the only way to get enough return air to the unit. In our case, adding extra intakes won't help because the restriction is the truss.
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Old 10-04-2018, 03:22 AM   #16
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Sorry for the late reply but I am having lots of issues getting the forum to accept a post from me. Sent the admin a message
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Old 10-04-2018, 11:38 AM   #17
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Quote:
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We found that the A/C return air intake is located on one side of a truss and the return air duct is on the other side of the truss. They cut slots thru the truss so the unit could breathe but they are way too small. Widening them is the only way to get enough return air to the unit. In our case, adding extra intakes won't help because the restriction is the truss.
Wow! That's just a big bowl of wrong.
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Old 10-07-2018, 06:51 PM   #18
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We found that the A/C return air intake is located on one side of a truss and the return air duct is on the other side of the truss. They cut slots thru the truss so the unit could breathe but they are way too small. Widening them is the only way to get enough return air to the unit. In our case, adding extra intakes won't help because the restriction is the truss.

guess i need to look up there into duct not much hope of fixing what is sealed into upper ceiling but it seems every time i look at a item to fix there is a little something to repair.

always

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Old 12-01-2018, 06:39 PM   #19
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One thing I have noticed on our 38rl while trying to find why air flow isn't what it should be is I have noticed that when I remove the vent covers and stick my hand in the ductwork that the four air ducts forward of where the unit is located in the living/kitchen area there seems to be a huge amount of air movement going toward the front of the trailer where if you do the same with the vents towards the back of the trailer there is not nearly as much as going the other way. It almost seems that it would be better if the air conditioner was located at the rear of the trailer where it could blow all the air in one direction instead of splitting it two ways.
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Old 12-06-2018, 02:54 PM   #20
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I've done all the improvements that have been discussed here on my RL - like cutting the collars and cleaning the filters, etc..

Last year, I added two additional return air intakes to each A/C using same factory grilles, etc. The additional volume of air was noticeable on the rear unit, but the improvement on the front unit was minimal. Turns out that the return air ducts are minimally sized and then the wire bundles passing through the ducts and the sprayfoam invading all the joints cuts down on airflow further. Seems like the add'l ducts would need to be closer to the unit, but then the noise will probably also increase.

Also have the lame airflow to the bedroom issue. It seems like the restriction (or leakage) is on the pressure side somewhere between the bathroom and the bedroom. Good pressure in the bathroom and then minimal flow from the bedroom ducts. While cutting the bedroom collars, I noticed that the air ducts continue forward and into the closet. That's a good 6 feet of additional duct beyond the last outlet. Not sure if they are even sealed above the closet ceiling.

Anyone ever seal off the ducts after the bedroom outlets, or add outlets in the closet ceiling at end of the ducts?
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