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Old 07-17-2013, 01:37 PM   #1
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3171DS Air Conditioner

Hi all. I just bought my 3171 (our first motorhome) and during the PDI I noticed the air wasn't blowing out the bathroom register and the one downstream in the bedroom. The dealer said they would look at it while we finished the paperwork.
Anyway, once we took possession I checked the air again with the same low air flow. With hvac experience in my background I thought either blockage or a leak in the duct to the attic space.
I had similar experience with my previous two TT basically sealing issues at the air conditioner to the ducts.
So I checked at the air conditioner first and found the FR did a 1st class job on sealing. I began removing the registers to peek in on the duct run.
What I found was quite surprising. The bathroom vent and shower skylight were framed into the duct. The skylight took about 1/2 of the duct run. From my view inside the duct it doesn't appear to be sealed around the frame of each of the openings.
That is one part of the problem. The other is the abrupt block in 1/2 of the duct to the back registers. My thought is to fish a sill plate gasket into the duct from the kitchen register (before the skylight frame) to the bathroom register. The duct measures 1-3/4" high so the gasket would need to be at least that in width. Then at each of the registers I would pull the gasket upright and conform it to the top and bottom of the duct and to the duct sidewall along the framed sections. This (ideally) would also help direct the airflow around the block of the shower skylight.
I was curious if anyone else experienced air flow issues and how did you go about correcting them.
Photos help detail the problem which I will post later.

Bobby
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Old 07-17-2013, 02:36 PM   #2
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#3051s

To cool down my #3051S quickly I close the sliding door from the kitchen to the vanity area. Then reach up to the A/C and open main register/louver. This greatly reduces the air flow to all registers but rapidly supplies the front of the RV with strong cooling air. It is noisy for a while but after things cool down just close the A/C main register.

BTW...I purchased two Dometic window awnings and had them installed on the large windows. My problem is reducing the heat coming through the three large skylights. I have an idea of something to be made like an inside vent cover when I return home in the fall.
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Old 07-17-2013, 02:57 PM   #3
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Thanks Tim. I do use the same air dump at the air conditioner which works well but my concern is with the air flow.
Good idea on the window awnings. I keep our share closed when sun is out.

Bobby
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Old 07-17-2013, 03:27 PM   #4
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Bobby,
I just counted 10 ceiling registers on my #3051S. Currently, I am camping in the mountains of North Carolina. The temperatures here have been decent with lots of rain. When the sun is strong in the afternoon my a/c unit runs hard to cool things down. The evenings are better because the outside temps drop nicely. But, I believe cooling this RV in 90 degree temperatures could be a problem. BTW...my registers seem to be working ok with all about the same flow rate. If necessary I may close the front ceiling registers if more flow is needed in the bedroom at night. Oh, I also run two small electric fans to keep a constant air flow.

I love the window awnings and got use to them on my Class "A". This is the first time I have left my main awning open but have two tie downs securing it safely in place. My rear window could not accept an awning because the mounting hardware would interfere with the ladder.

The large skylights are bringing in unwanted heat during the day. This is an issue I need to address.
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Old 07-17-2013, 04:38 PM   #5
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Tim, I agree that cooling the coach in 95+ degree temperatures and the high humidity is a challenge, even for the 15k btu air conditioner. I had a 31 foot travel trailer that I ordered with a 15k unit and it could keep the entire camper very comfortable even when we took it to the beach in the gulf south. The Forester appears to be better insulated than my TT was so that certainly should help.

I believe the 15k btu air conditioner is sufficient size for our Forester, the problem comes down to air flow. Consider air flow like water in a water hose. Restriction in the hose slows the flow, the slower the flow the longer it will take. An air flow restriction is in the same as cutting off the registers on the passenger side of your car but still trying to cool it down equally.
My back bedroom is the furthest from the air conditioner. The starboard side of the duct run has great air flow all the way back but the port side is just a faint flow. The same in the bathroom.

I finally have photos to show the vent and skylight cut-in of the duct work.
The first two are of the skylight and show the skylight framing and then the width into the duct. The third photo shows the vent and the small breach into the duct but no visible sealant. The ducts maybe 7 inches wide.

I thought of getting a windshield sunscreen to place across the skylight to reflect the light (and heat).

Bobby
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Old 07-18-2013, 08:58 AM   #6
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Quote:
Originally Posted by trwmodela View Post
To cool down my #3051S quickly I close the sliding door from the kitchen to the vanity area. Then reach up to the A/C and open main register/louver. This greatly reduces the air flow to all registers but rapidly supplies the front of the RV with strong cooling air. It is noisy for a while but after things cool down just close the A/C main register.

BTW...I purchased two Dometic window awnings and had them installed on the large windows. My problem is reducing the heat coming through the three large skylights. I have an idea of something to be made like an inside vent cover when I return home in the fall.
Personally I would do a snap/velcro on black out shade. Or, you can order a dual shade from our parts department I think. In the pacific northwest where I cover, people really want the natural light...but I guess in the southern states that can be an issue. I don't have part number, but a dual day/black out shade might be the ticket.
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Old 07-18-2013, 09:05 AM   #7
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Bobby, interesting seeing how the ducted flow is directed. My bedroom does have the weakest flow of all ceiling registers. I have a skylight over the vanity and tub in my #3051S. But the ducted registers run between both skylights in the vanity, shower area and rear bedroom. It appears there would be plenty of room to duct it correctly without skylight interference.
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Old 07-18-2013, 10:12 AM   #8
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Keep in mind the "ducts" are no more than cut outs in the foam core of the roof, which is mostly what the whole laminated roof is. It's not a true sealed duct system like you'll find in some non-laminated units. I prefer the way the cedar creeks are done, which is similar to the way our mobile scout was. In our forester, we too have a few ducts with some restriction, for probably similar reasons as mentioned. No big deal, as I think there are too many ducts to start with. We close off the few to increase flow to others. A lot of flow in fewer more strategically placed vents makes more sense than little flow in a lot of vents.
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Old 07-18-2013, 10:37 AM   #9
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Personally I would do a snap/velcro on black out shade. Or, you can order a dual shade from our parts department I think. In the pacific northwest where I cover, people really want the natural light...but I guess in the southern states that can be an issue. I don't have part number, but a dual day/black out shade might be the ticket.
So, this can be done for the skylight over the shower/tub? I've read before (not here) that blocking light within the skylight promotes UV decay(?). So I can do this and not impact the lenses of the skylight?
I would like to go this route if it will be safe for the plastics.

Bobby
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Old 07-18-2013, 10:44 AM   #10
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whoaaaa....I claim no knowledge of UV decay or its affects. I know BigJohn on here, painted and filled his without any issues.

I just know some people use a day/night or day/blackout shade. I know when I tinted my house windows they could not go bronze or mirrored since it reflects too much heat back into the thermopane gap. With a black out...its just reflecting it back into the space between the shade and skylight, not necessarily between the plastic panels.

The day/night shades that I speak of are only sized for the skylights. Since those are much larger areas. I'm sure you could get something similar for the shower, but we won't be stocking that.
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