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Old 07-13-2018, 11:23 AM   #1
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Portable AC Unit

Note: I tried posting to another similar thread but wasn't allowed to. Admins, please feel free to move if necessary.

We are in Florida and do most of our camping here and we all know how hot it can get.

Before I go on to explain the issue here are the details:

Rockwood 2703WS (approx. 28' box) with a 15k AC @ 30amp service. The campground pedestal has a 50, 30 and 20amp service. I'm connected to the 30amp. AC recently checked out (all good), filters clean, and there're no visible obstructions to the air intakes.

When temps are over 90 and we have no shade the AC struggles to keep 78 and just runs all day long.

So for this weekend @ Sanibel Island I borrowed my brother's portable AC unit that he uses for tent camping to help out the main RV AC.

After setting up yesterday the internal RV temp was 85 or so, and with both AC (RV and portable) going the temp got down to 80 in less than 15-20 mins. The portable AC was properly being vented to the outside. Total amp draw 22-23amps. However after that it just stalled at 79-80. A couple of hours later and well after sundown the temp was still the same. Checking the vents out of both units I could feel cool air coming out. So I turned off the portable AC and the temp got down to the RV's thermostat setting of 75 in a matter of minutes!

So was the portable AC basically undoing the work of the main RV? I went outside to check the portable AC exhaust vent and I could feel cool air being vented out. Reading the instructions of the portable unit it says a "small" amount of conditioned air will be used to cool the unit's compressor and vented out. It will also create a negative pressure within the area being conditioned (in this case my RV) potentially sucking outside hot air into the RV.

In any case, sorry for the long post, but just curious of others' opinion and experiences.

PS. There are two-hosed portable units that use outside air to cool the unit's compressor and do not create a negative pressure.

Thanks in advance!
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Old 07-13-2018, 12:34 PM   #2
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When temps are over 90 and we have no shade the AC struggles to keep 78 and just runs all day long.
Have you tried creating some shade? A "heat shield" consisting of a large tarp over the top of the trailer, spaced with some cheap beach balls, and secured like a "lean to" on the sunny side can block the sun and by keeping it off the trailer it allows some convection air current to keep from trapping heat.

Every situation may require some imagination and ingenuity to accomplish this but as long as you can keep the sunlight from hitting the trailer and still allow air circulation it will definitely help.

Not sure what kind of portable AC unit you have but the one I use in my house's bedroom works great without sucking in any outside air. There might be some slight negative pressure created in the house but due to it's size any effect is negligible. Might be a bigger issue when used in a smaller environment like a trailer. I'd be more inclined to improvise a "heat shield". Tarps and rope are pretty inexpensive, Just add a couple of painter poles, cheap inflatable beach balls, and a bag of tent pegs.
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Old 07-13-2018, 03:59 PM   #3
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My first question would be if you've checked your A/C units ducts, supply/return partition, registers, etc. to make sure that it's in the best shape possible? Especially check to make sure that the duct terminal ends aren't open and blowing air into the ceiling.
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Old 07-13-2018, 05:09 PM   #4
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Thanks Bama and Mike for your responses and definitely there r things to do to help the RV cooler (I already blocked the skylights and some of the side windows with reflectors and slide out toppers r on my list).

The AC and vents checked out ok and I believe the air is working fine but none the less another inspection may be warranted.

What I'm interested on is whether or not a secondary portable AC unit working inside the RV is working with or against the main RV AC unit. Any thoughts?
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Old 07-13-2018, 05:32 PM   #5
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Somewhat the same thing happened when my son borrowed my TT and took along a portable A/C unit he had. He put it in the back bunk room, vented it out the back window and on a very hot day the bunk room actually got hotter then without the portable A/C unit. After he turned the portable unit off the room got cooler. Strange. On your unit one thing I would check soon IF you have ducted air: Remove the ceiling registers, where the air comes out, and check to see if there is a gap between the duct material and the actual ceiling material. I have six (6) registers in my TT and when I checked them soon after purchase every one of them had a gap at that area. Two of them were large enough to put my index finger in the gap easily. I used aluminum tape to seal off the areas and I could tell a good difference as soon as I was halfway through. You may not want to hear this but with a 28 foot box and in the Miami area you may want to consider adding a second A/C unit. Mine is a 30 foot box with two slides in SW GA and I had to add a second 15K unit. It's so much better.
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Old 07-13-2018, 06:00 PM   #6
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Originally Posted by frankm View Post
What I'm interested on is whether or not a secondary portable AC unit working inside the RV is working with or against the main RV AC unit. Any thoughts?

I think the results you got are the answer.

In trying to "pump" all the hot air out of your trailer the intake air is heating the rest of the trailer up.

The portables with the tubes for discharge air are nowhere as efficient as the window units that have the compressor and condenser hanging on the outside of a window.

FWIW, I've seen a lot of small travel trailers with a small window mount installed in the bathroom window or off to one side of rear end of the trailer using a through the wall mount. If you don't want a second roof top unit the small units are quite inexpensive and cool small areas quite well.
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Old 07-14-2018, 09:07 AM   #7
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Originally Posted by Thurman View Post
You may not want to hear this but with a 28 foot box and in the Miami area you may want to consider adding a second A/C unit. Mine is a 30 foot box with two slides in SW GA and I had to add a second 15K unit. It's so much better.
Thurman, don't worry I have already thought about it and will call dealer for a quote

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In trying to "pump" all the hot air out of your trailer the intake air is heating the rest of the trailer up.
Mike that's thing, my understanding (backed up by the instructions) this unit doesn't pump the hot air out and bring fresh air in (as a air exchange unit would do), but it recycles/cool the inside air and uses "a small amount" of conditioned air to cool the unit's compressor and that's what it vents out.

I'm beginning to think it is the negative pressure effect that with a camper not fully air tight the portable AC is sucking hot air far quicker than both the RV AC and the portable AC can handle.

I've been reading about portable units with two-hoses vs one https://learn.allergyandair.com/port...-vs-dual-hose/ and it may be a better solution for my situation.

Thanks for the responses!
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Old 07-14-2018, 09:24 AM   #8
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We had a toyhauler and used a portable unit in the garage. It worked great, it cooled garage area nicely or even too cold. We ran it on a separate 30A power source. The main trailer living area never was great always a little warmer with the 15000 unit. The exhaust air from the portable unit was always warm even coming from a cold room.

Direct Myrtle Beach summer sun.

Did you run it through the camper or by a separate power source?? Personally I would not run it through the campers converter. Two ACs is going to run close to 30As

All I can say it worked great for us and recommended by our dealer.

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Old 07-16-2018, 08:38 AM   #9
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Originally Posted by Oaklevel View Post
We had a toyhauler and used a portable unit in the garage. It worked great, it cooled garage area nicely or even too cold. We ran it on a separate 30A power source. The main trailer living area never was great always a little warmer with the 15000 unit. The exhaust air from the portable unit was always warm even coming from a cold room.
Was the garage isolated from the rest of the RV, in terms of air conditioning? IE. It wasn't taking the RV's AC cold air out the exhaust vent like I was experiencing.

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Did you run it through the camper or by a separate power source?? Personally I would not run it through the campers converter. Two ACs is going to run close to 30As
I ran a HD cord to the pedestal's 20amp outlet.
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Old 07-16-2018, 11:01 AM   #10
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Install a second roof unit (if you have a empty roof vent), or a window unit & drop a cord to the pedestal as you are with the portable unit. Did that with a 35’ 5th wheel and it worked well. Coiled the cord on the ladder & used as needed.
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