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Old 06-20-2012, 08:20 PM   #1
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What to expect from 13,500BTU A/C

We're sitting in Phoenix on asphalt in an RV park. The air temp is about 108 today, and is expected to rise to 116 over the next few days.

The coach is a 24ft 5th wheel w/ a single slide.

After running 4 hours continuously, the inside of he coach is now "down" to 88 degrees.

The air coming from the A/C unit is 53 degrees.

I had a problem with the 20a A/C circuit breaker tripping every 10min or so, and ALL the breakers were warm to the touch (the 7300 converter temp was about 115deg with its little fan running). I checked the A/C draw and it's 17.8-18.1 amps continuous, a LOT when using a 20a breaker. The voltage at the box is 116vac.

By removing the converter box cover and aiming a small fan directly at the CBs, they are all cool now, and the breaker is not tripping.

1) Should a single 13.5 A/C be able to cool a coach like mine at 110 and above?
2) Is 18amps a lot for a 13,500 A/C? And if it's normal, shouldn't they have wired and protected it w/ a larger gauge wire and breaker?

Thanks,
Bob
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Old 06-20-2012, 08:29 PM   #2
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I have 2 A/C units in a 32 foot Class A & the most I expect is a 25-30 degree cool down to ambient temp. as long as the RV is cool the morning. I think a single unit on my RV pulls about 20 amps. RV's are really tough to cool in full sun at hot temps all day. The fact that you are getting 53 degree air seems to make me believe that your AC unit is running very well.
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Old 06-20-2012, 08:40 PM   #3
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Short answer is you need a second A/C if you are above 100 degrees for any period of time. You will have to sacrifice a roof vent, but they are an easy DIY install if you are familiar with wiring.

Continuous rating for breakers and wiring is 80 percent of maximum. That means 16 amps on a 20 amp circuit breaker with 12 guage wire.
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Old 06-20-2012, 08:42 PM   #4
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A 13500 btuh unit will typically draw about 15 amps. Make sure your filters and evaporator is clean. If you are getting more than 20 degF across the unit I would suspect low air flow. Run the fan on high with all vents open.

Shade is king, so shade all the windows. Also make sure it is bypassing air internally.

With the high ambients, the little unit may be doing all it can. 4 hours may not belong enough. Let the unit the all night and see how it catches up for tomorrow.

It is kind of hard to put a second unit on a25 ft. Trailer and add 50 amp service.

Ken
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Old 06-20-2012, 08:48 PM   #5
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As a general rule, air entering the air conditioner will be coole about 15 to 20 degrees, depending on the outside temperatur and humidity conditions.
For example, if the air entering the return air grilles in the air conditioner is 80 degrees F, the air leaving the discharge grilles in the air conditioner will be 60 to 65 degrees F.
As long as this temperature difference is being maintained between the return air and discharge air, the air conditioner is operating at its capacity.
If the desired inside temperature(normally 80 degrees F) cannot be maintained, then the heat gain of the RV is too great for the capacity of the air conditioner.

Parking the vehicle in a shaded area, keeping windows and doors shut and avoiding the use of heat producing appliances in the vehicle will help to reduce the heat gain.
When possible, the addition of insulation and tinted glass should be considered.

18 is a little high normal for a 13.5K AC is around Amps 14.0 cooling (at 95 degrees ambient)
With your higher outside temps AMPs will go up.

Keep the fan on the breakers.

A Coleman 13.5K Mach III PS only pulls 11AMP's.
I'm getting ready to order one of those. My 14 year old rear AC has only 10 degrees from intake to output now. Front still 15-20
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Old 06-20-2012, 08:52 PM   #6
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In Yuma in 90-100 weather we did just fine with one 13.5 heat pump. But a Newmar is better insulated than most and we have the optional roof insulation too.
Usually the delta between incoming air temp and outlet temp is within specs if it's 20's or so.
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Old 06-20-2012, 09:27 PM   #7
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Quote:
Originally Posted by bobinyelm View Post
1) Should a single 13.5 A/C be able to cool a coach like mine at 110 and above?
2) Is 18amps a lot for a 13,500 A/C? And if it's normal, shouldn't they have wired and protected it w/ a larger gauge wire and breaker?
Hi Bob,

I wouldn't expect a single 13,500 BTU A/C to come even close to doing the job in the direct sun at 110-115 degree outside temps. Having a 24' unit helps but then again the slide doesn't help. If you are going to be doing a lot of living in that environment and want to be truly comfortable during the day then you will in all likelihood need to install a second A/C, but as TXiceman said that may be difficult on a smaller unit so by all means try shading windows and all possible passive means first and maybe you can squeak by. If you get a good head start early in the day and shade the windows you might find the late afternoon tolerable, then when the sun goes down you should be OK.

As has been mentioned 18 amps is somewhat high for a 13.5k unit, but then again you are in pretty extreme conditions. If you are really seeing a 35-degree differential between intake and output air temperature then that would be a little too good to be true and I'd agree with the advice to check for restricted air flow. First be sure you do your measurements directly at the intake and output ducts to be sure you have an accurate reading.
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Old 06-21-2012, 09:07 AM   #8
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Thanks, all.

We went out visiting for about 6 hours, and returned at 10pm when the outside temp was down to an even 100 deg, and the RV was a comfortable 68 degrees.

The trick today will be make sure the unit can maintain the "cold-soak" we induced (that overcame the heat-soak we had yesterday).

If it were cooler when we leave daily, we could retract the slide and give the A/C a break.

A second A/C isn't that practical on our short 5er, and I would never choose to be in these temperatures (this is a family function or we wouldn't be here now), so hopefully this is a one-time deal.

I'll check the amp-draw today when it's cooler (it's only 80 this morning at 7am), and will keep the fan going.

Bob
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Old 06-21-2012, 09:36 AM   #9
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Parking the vehicle in a shaded area, keeping windows and doors shut and avoiding the use of heat producing appliances in the vehicle will help to reduce the heat gain.
When possible, the addition of insulation and tinted glass should be considered.
I would also suggest reflective foil insulation on the windows. You can get this at any hardware store in a roll. Where we are park in the Texas Rio Grande Valley in the winter, the back windows are constantly in the sun. We cut to size, pieces of foil for the back windows and used some of those Commander 3M velcro strips to affix to the windows. When we want to take them down, we only need to unzip the velcro strips.
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Old 06-21-2012, 09:44 AM   #10
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The best thing you can do in this heat, especially since it is temporary, is shrink the space that needs cooling as much as practical. Bringing the slide in will help, as will closing off the sleeping area if possible. Any areas that you don't NEED to be cooled during the day. Just make sure to open the sleeping area back up about an hour before bedtime to let it cool. If you can get some sort of shade, that will definitely help. We have mylar bubble wrap on all the windows which blocks a lot of heat and light. We use LED lights to minimize heat from our lighting (you'd be surprised at how dark it can be in the daytime with the windows blocked). If it's just for a few days, do what you can and grin and bear it. If a week or longer, the mylar stuff will be very useful to you. It comes in rolls at Lowes or Home Depot and will cost ~$20-30 to do all of the windows. You can always pull it out when the heat drops in the evening.

Just some thoughts. Best of luck!!


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I would also suggest reflective foil insulation on the windows. You can get this at any hardware store in a roll. We cut to size, pieces of foil for the back windows and used some of those Commander 3M velcro strips to affix to the windows. When we want to take them down, we only need to unzip the velcro strips.
I must type a bit slow, since I didn't see this one before posting. What I quoted is exactly what we did last year. Only problem is that the heat is so strong, it is beginning to melt the adhesive on the velcro.
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Old 06-21-2012, 09:50 AM   #11
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We went out visiting for about 6 hours, and returned at 10pm when the outside temp was down to an even 100 deg, and the RV was a comfortable 68 degrees.
That's because it was dark, as radiant heat from the sun makes all the difference in the world. But if you use the 'cold soak' technique in the morning that will probably get you through the worst part of the afternoon in halfway decent shape, or at least something you can live with on a temporary basis. And it sounds like you already know the best answer of all... your house has wheels, so just don't be where it's so hot.
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Old 06-21-2012, 10:01 AM   #12
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I would also get a 30A to 20A conversion "bone". When using 20a you have about 2200 watts of power available and if you are popping your breaker you are close. At 30A you have 3300 watts which gives you a much larger margin before the breaker trips. A cheap way to help cool your unit down with only one A/C is to use a flying tarp over the trailer to keep the sun from baking the RV. A set of 4 folding poles, a 15' X 25' blue tarp and some lines to put it up about 2 feet above the rv and you have air shield between the tarp and your RV top. Cheap and it works.
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Old 06-21-2012, 10:03 AM   #13
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And it sounds like you already know the best answer of all... your house has wheels, so just don't be where it's so hot.
I thought we raised our kids "right," but two of them somehow thought that living where you can fry eggs on your car's dashboard in Summer was a good idea!

Maybe after 10 years in Alaska as kids, they just wanted a change.

Bob
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Old 06-21-2012, 10:06 AM   #14
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I would also get a 30A to 20A conversion "bone". When using 20a you have about 2200 watts of power available and if you are popping your breaker you are close. At 30A you have 3300 watts which gives you a much larger margin before the breaker trips. A cheap way to help cool your unit down with only one A/C is to use a flying tarp over the trailer to keep the sun from baking the RV. A set of 4 folding poles, a 15' X 25' blue tarp and some lines to put it up about 2 feet above the rv and you have air shield between the tarp and your RV top. Cheap and it works.
We have a 50a RV outlet feeding the RV through a 50/30 dog bone.
The 20a breaker that was tripping is the individual breaker for the A/C circuit in the RV's converter box.

The shade is a good idea, but we're in a RV park where the logistics of the assembly would be tough, assuming the park manager didn't go apoplectic at the sight of it.

Bob

BTW, I checked the amp-draw this morning, and it was down to 13 amps.
The hot temps messed with EVERYTHING I guess!
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