New AC returns added

**piper guy** · 03-06-2022, 07:04 PM

For any of you that have a two AC coach, this mod is an incredible one. Might also be appropriate for a three unit, but I’m not sure how the ductwork is on those.

One of the guys on the Facebook Redwood group is an HVAC engineer and came up with this. Also validated before and after airflow and Delta T temperatures. Difference is amazing.

I did our 36RL yesterday and can verify that supply air into the coach at least doubled. I’m going to add another 4 outlet vents as soon as I can get them ( the one place I checked that had them is out of stock). There isn’t any increase in noise in the coach other than maybe a little more air flow noise.

You’re cutting into the return ductwork and adding a filtered 10”x14” return grille to both units. Down the road after I get the additional outlets installed, I’m going to block the ductwork and turn the coach into a true 2-zone unit with separate ductwork and AC unit for main living and bedroom.
Took me about 2.5 hours start to finish. Most of the time was spent cleaning inside the plenum after cutting the ceiling. There is so much “ stuff” routed through the returns that it’s amazing there was much of any flow at all. It’s also a great time to check the foam closing off the return and supply plenum. You’re right there and can see it.

Have fun guys !! Hers another mod to add to the “putter list”. lol

My apology for the sideways picture. I haven’t figured out how to stop my iPad from turning it.

XCMARK · 03-12-2022, 07:10 PM

Did your AC system have two factory return vents on each AC? Our 2015 has 4 returns one on the left and right side of center in roughly the same location as the vent in your photo. I am trying to decide if this is needed since we have 2 returns now. I know airflow is a problem on these systems and most trailer have the hot and cold divider falling out and letting the air short cycle right back into the AC unit , I fixed ours last spring ( very noticeable improvement).

Mark

**piper guy** · 03-13-2022, 03:39 AM

Mark - I can’t take credit for this mod. Yes, my 2013 has two returns for each unit. Problem is, whoever initially designed it, did not do it right. Not nearly enough flow. Way too much restrictions in the return ductwork.

One of the members on the Facebook group is a HVAC Engineer. He looked up all the specs for theses units and they are capable of 350 cu/ft per minute. He put a flow meter on and got 190. When this mod is done, flow went to over 320. You can feel the difference in the coach. With both units running it will blow the shades around now. After I add some more supply outlets, I’ll block the supply trunks to separate the front and rear units totally and zone the systems.

drj564 · 03-14-2022, 01:58 PM

Oh wow thanks for posting this. I got rid of my FB account so I never would have saw this. Such an easy mod with great benefit. Household filters to boot! I’m definitely doing this one. Our 2018 39MB has 3 AC’s and the front and rear ducts are already separated. But this will definitely fix the cooling issues!!!!! Thanks again.

Edit: Was looking for 10x14 and these are hard to find. Where did you get yours?

XCMARK · 03-14-2022, 09:21 PM

Quote:

Originally Posted by drj564

Oh wow thanks for posting this. I got rid of my FB account so I never would have saw this. Such an easy mod with great benefit. Household filters to boot! I’m definitely doing this one. Our 2018 39MB has 3 AC’s and the front and rear ducts are already separated. But this will definitely fix the cooling issues!!!!! Thanks again.

Edit: Was looking for 10x14 and these are hard to find. Where did you get yours?

make sure you remove the top sheetmetal , the black foam is glued in and many owner have found the air crosses from the discharge side right back into the return air stream. 3 Ac units will not have a problem keep thing cool unless this issue has happened in your RV.

**piper guy** · 03-16-2022, 03:35 AM

Mark - no need to go up top. When you cut this opening, you’re in the plenum. Just look up and check the divider and make sure it’s secure.

**piper guy** · 03-16-2022, 03:37 AM

Note - I got the 10x14 on Amazon. Took a while to get them. A 10x12 has also been used successfully.

gossamar · 04-10-2022, 02:51 AM

Piperguy...is this a different mod from the ones completed last year in the post "ac not keeping up?". I can't remember who posted the original mod back several years ago, but Rob FLA revisited the mod and added the front cap insulation addition as well. I added 4 10x10 vents, 2 on each AC unit and it made a huge difference. I am seeing over 20-degrees delta with one ac working and 25-30 degree delta when both are fired up. Here is a picture of one of the returns added.

drj564 · 04-10-2022, 03:31 PM

Quote:

Originally Posted by gossamar

Piperguy...is this a different mod from the ones completed last year in the post "ac not keeping up?". I can't remember who posted the original mod back several years ago, but Rob FLA revisited the mod and added the front cap insulation addition as well. I added 4 10x10 vents, 2 on each AC unit and it made a huge difference. I am seeing over 20-degrees delta with one ac working and 25-30 degree delta when both are fired up. Here is a picture of one of the returns added.

So apparently the electric restrictions going through the original duct are not that restricting? Or did you do something else to open that up?

The first post puts a return air directly under the unit which I’m afraid of the increase in noise from the ac unit.

**piper guy** · 04-10-2022, 03:33 PM

Similar in that you’re going into the main return plenum. Just using one larger vent.

As you mentioned, difference in flow and delta T temps are considerable. I’m in the process of adding 6 more outlets. The units have the capability of flowing much more air. The original design sucked.

**piper guy** · 04-10-2022, 03:34 PM

And as to noise- the units are, in my opinion, actually quieter.

drj564 · 04-10-2022, 03:41 PM

Quote:

Originally Posted by piper guy

And as to noise- the units are, in my opinion, actually quieter.

This is good to know. When I’m running all 3 units (really it’s the 2 units in the living kitchen area on same track) our rig is pretty loud. I suppose that’s from the restricted air then.

gossamar · 04-10-2022, 07:32 PM

Piperguy....I got it now.... Drj564, the electrical restrictions on airflow are most likely still there is some capacity, but I think the overall crushed return ductwork where it crosses the supply on each run was the bigger culprit. Cutting the extra 10x10 vents allowed me to re-enforce that section with rigid styrofoam. As I added two of these 10x10 to each side, air return supply was greatly enhanced. As noted, I have enough supply vents as Crossroads must updated the design at some point prior to mine being built. I wonder if other Redwood/Rushmore units were also updated during this time with the additional vents. If I remember, they moved the Rushmore line from the Redwood line sometime in early 2015 before they discontinued the product line?? I actually have a Redwood sticker on the frame of my coach on the door side.

drj564 · 04-22-2022, 01:04 PM

I received my filtered return air grills and installed the first one yesterday in the bedroom. I cut a small hole in the ceiling between the 2 factory intakes which is where the pic shows in the first post. I expected to see the intake inlet for the the ac unit directly above but no. It’s in the next bay and the air flow goes through the aluminum roof support. Redwood cut holes through part of the support for the air to flow through but these just don’t seem like a lot of air volume will pass through. Maybe I’m worried about nothing with flow restriction? I assume they are all like this?

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