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Old 09-14-2014, 05:34 PM   #1
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Weak rooftop a/c

You guys always have lots of good advice so I'm back for more. My rooftop a/c works fairly well as long as the temps are below about 85 degrees. Here in Oklahoma summer days can easily get above 100. We bought this MH mainly to use as resting place during motocross events but the a/c is not up to the task. Most of the tracks have no shaded areas to park. It has been cleaned, condenser and intake, which helped some but not enough. Filters have been replaced as well. The fan only works on the high speed setting anyway. Should we just replace this one with a new model or maybe add a second unit if possible? This is the original unit that came with the MH. Dash air doesn't work (yet!) so I'd like to have as much air as possible from the rooftop(s) What have you guys done for more air?
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Old 09-14-2014, 07:45 PM   #2
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Using a thermometer check to see how cold the air is that it's producing. Anything over an 18 drop from ambient and the unit is cooling within spec.

You should consider window coverings that prevent sunlight penetration.
You could add another unit to the roof.
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Old 09-14-2014, 07:59 PM   #3
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Something else to look at is whether the incoming and outgoing air are being allowed to mix/short cycle due to missing/wimpy/poorly installed baffling within the plenum (the part that hangs down inside).
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Old 09-14-2014, 08:13 PM   #4
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I remember renting one of those coaches years ago, and during the trip in the NC State Park, Wilmington, the A/C unit had to remain on during most of the time we occupied the coach. This was in 90 plus degree weather. Other than that we loved the coach and enjoyed our stay.

I'm thinking you have an insulation issue that you may or may not be able to address. I'm not sure what size A/C unit is installed but if it's a 13K btu unit, you can do better by replacing it with a 15K btu unit. Yes you could add another unit, and I'm sure with that size coach, you would have no problems keeping it cool.

But if you're boon docking at a race, I'm assuming you are not plugged in to an outside electrical source. Your gen set will be heavily taxed running two gen sets, if it can run two at all. Don't count on any reserve power for anything else, and be sure to show up to your site with a full tank of fuel. I've used an 8KW aux portable gen in the past when faced with that issue. You may or may not have that option.

But that's just a start, you really need to first figure out a way to some how increase the effectiveness of the insulation. Some have used blow in foam in the can into void areas between the coach skin and the interior. But you really have to know where the empty spaces that let the outside heat transfer to the interior are and not cause interference problems.

I'm sure this, with along with other posted suggestions help you successfully address your problem.
Good Luck
DTW
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Old 09-14-2014, 10:00 PM   #5
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The air feels decently cool from the outlets, just doesn't feel like it's moving enough of it. I can't detect any mixing in the plenum by putting my hand up there. This is a 13k BTU unit. I've priced the 15K BTU units and they're on sale right now for about 650 to 700, depending on where it's purchased from. We do use an external genny when at the tracks, its a Honda Black Max 7500 continuous/8500 max. We also carry a smaller 3.5K that powers the a/c & lights in the trailer that we have the bikes in. So I think we have plenty of power. My on-board Onan 4k is waiting for a new control board. This is our first MH and the plan is to upgrade in a year or two so we don't want to spend a fortune on this one. The next one (longer) will be the real money pit! But man it's nice to be able to park a class A in a parking spot at the grocery store. Who knows I may just keep it long term. I kinda like it! So you guys think a 15k unit alone would be enough?
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Old 09-14-2014, 10:23 PM   #6
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We used to have an 89 Southwind 30'. It took 2 13.5 K ACs to keep it cool in Texas summers. Those older coaches don't have the insulation of the modern ones. I had to rig one of the mods to run 2 ACs at the campgrounds.
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Old 09-14-2014, 10:48 PM   #7
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Dtwallace you are absolutely correct on the insulation issue. I have no idea what's in these walls but it can't be much. We have a clock with temp & humidity mounted on the wall above the entry door and when the sun is on that side I've seen it read over 110 degrees when the outside temps were in the mid 90s.
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Old 09-15-2014, 09:18 AM   #8
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Our 1989 RV always had problems keeping the front area cool in hot weather, due to the large front glass area. When the front roof AC died I replaced the old 13k BTU unit with a 15k unit. The new one solved our problems and dash AC needs were greatly reduced. The new AC unit required a remote (new) thermostat and related rewiring. Not a big job but needed for the newer model. Dometic nicely provided the support & part numbers.
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Old 09-15-2014, 08:00 PM   #9
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I really like those older class (C) coaches, and if it was mine, I'd try the foam insulation in the can first. That's unless we hear from another contributor here why this would not work.

I have a 24 foot utility trailer that just happens to have that type insulation in the walls. At one inch thick, it's amazing how it maintains a stable temperature inside and without any cooling or heating devices installed.

You may have to experiment with the can a little to figure out the best way to get it to form in the wall without making a mess, and how much to use for the space you're trying to fill. This stuff expands and if you put too much in too small of a space, it will push your wall out of shape, don't ask me how I know that, LOL...

You'll find methods of introducing it into your walls on the can, as where the most used is to drill a small hole in the spot you will stick the straw. It does spread out, but its best to start it as deep into the space as possible. I've used a nail to make the hole.

Once a can is opened and put in use, that can, cannot be stored for future use. How you then cover the entry holes is the next consideration you have to deal with if you decide to try this insulation. It's not expensive to try, but it takes a little forethought as to how you apply it. I've used tape over the hole to keep the foam from coming out until it dries. If you get it on your wall on the out side, it can be wiped off with a rag before it dries. If it dries, it can be scraped off with a blunt object in most cases without damage to the finish.

Wishing you the best
DTW
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Old 09-15-2014, 10:55 PM   #10
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Well after giving my idea of adding a second unit a lot more thought, and reading all the responses from you guys, I have decided not to try it. I am going to purchase a new unit to replace the existing one. I'm going to go with a 15k BTU unit. Now for a little research to try to get the most efficient. Thanks to all of you.
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Old 09-16-2014, 01:47 AM   #11
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I have an '88 Itasca Sunflyer 22' here in Phoenix. The walls of our coach have blue foam insulation in them. The rooftop a/c will cool the interior to well over 100 degrees.
I did insulated the front of the coach under the hood with the silver rolled insulation. I did this because one December up in the mountains we had a snow storm come in and I could not believe the outside air infiltration into the cab area! Had snow on the inside!
You might check the air temperature coming out of the unit and if over about 40 degrees you could have a faulty thermostat. You can jump the wires on the thermostat to see if the unit is capable of getting colder. Should go below 32' easily if the outside temp. is not above 80 degrees after it has run awhile.
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Old 09-16-2014, 06:19 PM   #12
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The easiest way to find out where to put your insulation is to go to a person or agency that does energy audits, they have a camera that will take pictures of where your deficient and have leaks (air not water)
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Old 09-19-2014, 03:49 PM   #13
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I saw where you have decided to buy a new 15K roof air. I saw on youtube

Mini Split A/C on a Rv Camper. Better than a roof top or a window unit! - YouTube

someone using a mini split AC unit for his RV. $400 bucks. That might supplement what you have now and would be less expensive than a new 15K.

I would start with putting some kind of insulation on windows, like reflectrix on side windows and an outside insulating cover for front windows. Maybe your existing will work with proper insulation.

Anyway, looking forward to seeing what you end up with and how it works.

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