Is one AC better than another?

[Silverback1]

Hi folks,
I have a fairly new Dometic Duo Therm on our '75 Tradewind (25 '). I'm not sure of the BTUs, but I do know that it struggles in the afternoon sun here in South Florida. My wife wants to add a 2nd unit, but I suspect we just need to change it out for a beefier model (15,000). My paperwork doesn't specify the size. I have 2 questions:
1. How can I verify the BTUs of the existing unit?
2. Is one brand of AC better than another? I read that Coleman uses all copper tubing. I like the idea of remaining with Dometic, but I'm not afraid of switching allegiances. Also, I need to stay within my 30A capabilities.
--Jim

[blkmagikca]

There are two aspects of air-conditioning: cooling and dehumidifying. Some time ago I had a SOB 19.5 foot trailer and I put a 13,500 btu a/c on it. I should have used an 11,000 btu unit, as it cooled down rapidly but didn't get the humidity out. Thus, for a 25-foot trailer 13,500 btu is plenty.

Having said that, however, if the trailer was in use in southern Arizona where summer temperatures regularly go up to 110F and there is lots of sun and no shade, I would consider opting for a larger unit.

[goshawks00]

So then , if I may , how do you go about determining the correct humidity AND cooling abilities of any unit... Having one cool great but not remove humidity isn't good. I have a 22' Safari and am also looking for an AC
unit that will work for us .
Thanks,
Barry

[chiefneon]

Howdy!

Recently our Coleman 13500 AC had to be replaced. The RV repair had a new Dometic 13500 and installed it. We found out the Dometic would only cool to 70 degrees and the compressor would kick off. Temperature would go up to about 74 before the compressor kick on and started cooling again. This was not comfortable at night in the Texas heat. RV repair check the unit during the daytime and found it to be cooling correctly. They contacted Dometic and Domectic conformed the new unit would only cool to 70 degrees. We are now waiting on a new Coleman unit to arrive to replace the Dometic. Coleman states their low cutoff is 60 degrees.

"Happy trails"
chiefneon

[perryg114]

I solved that early cutoff problem by locating the temperature sensor outside the intake box. There are always leaks that cool the intake air below the temp in the trailer and the thermostat cuts off early.

I am not sure that a 15k unit would solve all your problems. In FL heat you need to have awnings and you need to make sure you don't have any open curtins that are facing the sun. Polishing the roof to reflect the sunlight should help a lot. Dark backed curtins are also a no no. Anything you can do to shade the trailer is going to help you. Reflective window tinting is going to help you a lot.

Measure the temp difference between the intake and the outlets. You should get about 20F difference between the two. Less than 15 deg and you have a bad unit or one needing repair. Check to make sure the evap coil is not full of dirt. This is the one that cools and the one the air from the trailer passes through. Usually you can get up there is a crevice tool on a vacuum.

On a hot day I would not expect it to get much below 80F in the trailer unless you are in the shade.

Perry

[idroba]

On the size of your current unit: You should be able to remove the interior air cover/box and expose the guts of the beast. Somewhere there will be a manufactures tag with the btuh rating on it. You may have to look a bit, they hide them well sometimes.

[Silverback1]

Thanks for the quick replies, everyone. Perry,we have excellent awnings all the way around, along with pull down shades on the inside. The unit works well: cycles on and off; blows cold. It just doesn't seem to cool the whole volume. I'll let everyone know how things shake out. Thanks again. I really appreciate your time.

[richinny]

i hear that miami is getting a rather hot summer already. are you running the fan on high to prevent icing of the condenser coils?

some people have had success with sun block panels that go on the outside of the glass. any chance of a spot with shade?

[perryg114]

If the unit is cycling on and off then it is not going to keep the temperatures under control. I would move the thermostat sensor outside the air box. I had this problem with the old Coleman and my new Dometic Unit. You can always hotwire the thermostat so it stays on 100% of the time. You can multiply that BTU rating by the percentage of time it stays on to get an idea of what the actual BTU rating is. If it stays on 50% of the time you are only getting 13.5k/2.


Perry

[blkmagikca]

Originally Posted by goshawks00

So then , if I may , how do you go about determining the correct humidity AND cooling abilities of any unit... Having one cool great but not remove humidity isn't good. I have a 22' Safari and am also looking for an AC
unit that will work for us .
Thanks,
Barry

This would come under the purview of a heating/airconditioning/ventilation engineer. I just remember that with the old SOB I regretted not having purchased the 11000 btu unit. I had been told that it would take longer to cool down, but that it would remove more humidity.

I wonder what size a/c Airstream is now using for the Bambi's.

[perryg114]

It really depends on the temperature and humidity of the enviroment you are in. If it is 70 degrees and 80% humidity I doubt any unit is going to run long enough to lower the humidity. What the HVAC guys do in that situation is to add heat to the air flow so that the AC stays on till the humidity is say 50%. I don't think your average AC unit is going to be this advanced though.

Yes a smaller AC unit might control the humidity better in cooler climates but it is going to suck in the FL heat. The problem is you never know what you are going to be faced with. If you have the power you can run a small heater in addition to the AC to cause the AC to run longer to remove more humidity. You could also run a dedicated humidifier which amounts to another AC unit.

Perry

[overlander63]

Originally Posted by Silverback1

Thanks for the quick replies, everyone. Perry,we have excellent awnings all the way around, along with pull down shades on the inside. The unit works well: cycles on and off; blows cold. It just doesn't seem to cool the whole volume. I'll let everyone know how things shake out. Thanks again. I really appreciate your time.

Something to consider... I took a page from current production, and painted the center roof panel white on ours. The white color reflects more heat than the silver color, and the stuff I used (Kool Seal) also helps insulate, and covers a bunch of potentially leaking rivets. We have a 13500 btu on our 31', and it is adequate for most use. Last weekend, it worked well in the 102+ heat, at least until the power at the campground went out.

[perryg114]

Polished aluminum should reflect the heat as well as a white roof. However, white beats oxidized aluminum every time. White paint I would think would be prone to mildew especially in FL. I would think it would require bleaching a couple times a year unless it has something like Arsenic in it to retard mildew growth.

http://rmico.com/coatings-specificat...e-aluminum-bal

Perry