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Old 11-10-2020, 09:02 AM   #1
Winnie-Wise
 
Join Date: May 2020
Location: Sugar Land, TX
Posts: 385
Improving A/C Duct Air Flow and Reducing Noise

Recently, we've seen multiple YouTube videos posted about a new product from RV AirFlow that claims to improve air flow, improve cooling and reduce noise.

They've developed what appears to be a styrofoam insert that is installed into the roof air conditioning plenum the routes all air into the ceiling ducts, eliminating backflow (cold air from the A/C being sucked immediately back into the return), and reducing noise (because the insert adds sound insulation below the fan.

It looked like a great and simple idea.

We were getting ready to order one - and then went out to measure the A/C plenum in our 21VD and determined Winnebago's configuration doesn't match the specific measurements used to build RV Airflow's product.

I reached out to them, and they confirmed the current product works with some Grand Design models (they have an exclusive agreement allowing Grand Design to install their product at the factory) and that they wouldn't start working with Winnebago until next year.

Rather than waiting until then, I thought I would make a pass at a short-term solution, and if that wasn't good enough, we would purchase the RV AirFlow product when they had a version that worked with our View.

Using HVAC tape and a roll of duct insulation (sticky on the back) from Home Depot (at a fraction of the cost of RV AirFlow's product), I spent less than 2 hours yesterday working on our A/C plenum.

I removed the outer face plate and the inner face plate (4 phillips screws each).

I noticed the divider between the output and input sides of the plenum had already started to flop over into the input side - cold air was being sucked directly back into the A/C unit - which reduced the air flow actually going into the coach.

I removed the divider and reinstalled it in the correct position using the HVAC tape - taping it to the top and sides of the plenum - on both sides of the divider. One side of the divider is unfinished - I placed this on the bottom (where it would sit ontop of the inner face place) and used HVAC tape to seal that bottom.

Using HVAC tape, I then sealed the output side of the plenum underneat the fan. This eliminated some small air gaps where air was leaking.

The next pass was to cut the duct insulation and completely cover the inside of the output area of the plenum, leaving holes for the fan (in the top) and the two side ducts. I then used more HVAC tape to seal the edges of the duct insulation.

On the top side of the inner faceplate, I covered the area under the output side of the plenum with duct insulation - closing off the air dump vents that are part of the A/C unit - which will force 100% of the air from the A/C into the ceiling ducts.

I installed the inner faceplate and then turned on the A/C system in FAN HI mode. I added some HVAC tape over the top of the screws on the output side, since that area had small air leaks - and with the increased pressure inside the plenum, since it was now sealed and forcing air only through the ducts, the small air leaks could be heard when standing under the A/C.

I also installed a layer of the duct insulation to the outside of the inner faceplate, on the output side of the plenum (where there is the large hole intended to provide air to the dump vents). I did this to provide additional sound insulation, and also to ensure no air was working out underneath the duct insulation installed inside the plenum.

I also put my hand into the input side of the plenum and felt around the divider to verify there wasn't any air leakage from the output side of the plenum.

And then reinstalled the outer face plate.

Since I didn't make any quantitative measurements on air flow out of the ducts or measure the sound level, I can only provide subjective results.

After doing this work, the fan noise seems much lower and the air flow out of the ceiling ducts seems much better. I also suspect the air conditioner will cool better, since 100% of the air flow is now going into the ducts - eliminating any leakage that was going directly back into the air conditioner.

We'll go on our first trip with the improved A/C this weekend, and see if it really has had an impact.

While this requires a little more work than installing the RV AirFlow product, their installation does have one step that could pose a challenge to most RV owners - they require remove the 4 long bolts holding the air conditioner onto the roof - and actually recommend shifting the air conditioner, if needed, to get everything to line up with the holes they have in their product. And then when you reinstall those bolts, you're supposed to torque the bolts to the level recommended by Coleman - something most owners won't be able to do without purchasing an extra tool.

If the changes we made are "good enough", they can be done with only a screwdriver and scissors - and doesn't risk moving around the air conditioner on the roof... Plus at a much lower cost!
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Old 11-10-2020, 09:09 AM   #2
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Join Date: Oct 2019
Location: Sacramento
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Excellent writeup and great tips for improving air flow. ON the Vita & Porto I found the air channels go way past the vents. So I blocked the air channel extensions off with Styrofoam where the air goes no where. I also payed close attention to the channels coming off the main unit. I found they had not been cut out properly which was blocking air flow to the vents. The main idea is to have as few obstructions as possible for air flow and no leaks.
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Old 11-10-2020, 11:44 AM   #3
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I saw a video of someone fixing the porting on their interior AC years ago. It's been done before by others. Good that you saw it, and decided to DIY it. Saved you a ton of money and grief, for sure.
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Old 11-10-2020, 02:13 PM   #4
Winnie-Wise
 
Join Date: May 2020
Location: Sugar Land, TX
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I watched multiple videos on making the same changes before attempting it.

And suspect that DIY may be good enough - and much less expensive than buying something like the airflow product.

Grand Design has recognized the A/C plenum problem - and is now installing the airflow product in their new RVs.

With such a poor design - Winnebago really should follow Grand Design's strategy - and implement a solution at the factory.

The A/C was so loud in our 21VD, that with the stock TV at 100% volume, we still couldn't hear it when the A/C was running on lo fan... And the ceiling ducts don't provide enough circulation to cool the RV in the Texas heat...
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Old 11-26-2020, 02:22 AM   #5
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Great ideas, and I will certainly check ours out. However, might anyone have any pics of the process or a link or two to some good videos on the subject?
Thanks
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Old 11-26-2020, 06:21 AM   #6
Winnie-Wise
 
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This video illustrates the issue with the divider.

The plenum design for the divider allows it to be pushed relatively easily into the return side of the plenum, causing air gaps that forces the output air from the fans immediately back into the return side - robbing the coach of much of the circulation.

Once you have the covers off, using a combination of HVAC tape (not duct tape) and duct insulation (with sticky back), you basically tape the divider into place on both sides to prevent it from moving, and then using a combination of the tape and insulation strips cover the entire inside of the output side of the plenum (including blocking the hole on the plastic cover going to the air dumps in the cover), leaving holes only for the fan output air and the two side ducts.

Once you have the plastic covers off the bottom of the unit, it should be easy to see what needs to be covered.
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Old 11-27-2020, 01:01 AM   #7
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Thanks, love this guys videos. Very easy to follow and practical tips and tricks of the trade.
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Old 12-01-2020, 02:16 PM   #8
Winnebago Owner
 
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Posts: 149
An update with pics

Well, I pulled the covers off of both of my ACs and thought I'd give a report on how it went. I've included pics.

Disassembly is as easy as it appears, on mine, there are the four screws around the perimeter and three smaller ones, under the filter cover. Remove all of them and it drops right down.

What I found on the inside was the interesting part. Although nothing was out of place, meaning that the parts (baffles?) in question were in place and just need securing, the AC was filthy! The piece of sponge rubber that passes as a filter (and I keep it clean(!), is a joke. The only thing it filters is small animals.

I had on hand a small shop vac, a radiator brush and an air compressor and used all three. I first used the vacuum with a soft brush attachment and gently vacuumed the coil/condenser(?). I then went over it with the radiator brush, and vacuumed again. Then on the squirrel cage blower, I used compressed (low pressure) air and removed the dirt from the fins.

I then took some (window and door) spray foam and filled in a couple of cavities in the Styrofoam from manufacturing. I'm not expecting any trouble with the wiring and if need be, the spray foam should come right out.

Last I taped everything in place as described in the previously mentioned video. Might not be a pro taping job but I'm sure it will work.

As a side note, I suspect that the flow through my AC was restricted more by the amount of dirt than by any amount of deviation of the baffle. Final note is that the front AC was 10 time more dirty than the rear. The rear took no time to do.
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