Rooftop AC performance questions

[dufferDave]

Does anyone know the rough BTU-rating for my rooftop AC?

We have a 31-ft Fleetwood class C with an Airxcel AC unit (7000? 8000?). The RV is a 2003 model and the AC looks like original equipment. It's supposed to be a sealed unit, with little or nothing to fiddle with, and either runs or it don't. When we bought the RV the AC was indeed running but we only checked it for a few minutes of operation. (OK, so I was not super diligent.)

More recently we finally got a 30 Amp plug installed at the house where I can plug in to get "full power" for a day or two without having to run the on-board generator (and go through gobs of gas). Now I find out that the AC does NOT run....at least, not well. After 20 or 30 minutes I still cannot feel any substantial cooling inside the RV, and overnight the AC trips its circuit breaker and shuts off. This is NOT gonna make Mama happy if we go camping in the summer heat.

I am already planning on taking the whole thing back to our local shop when they open this week, but I wonder if I should just skip straight past trying to do anything with a 16-yr-old AC. I could go directly to a new 15,000 BTU AC that should provide plenty of cooling. I do not know if this would mean rewiring for a 50 Amp vehicle, or any other major side effects.

My wife has medical side-effects of chemo and radiation treatments and requires lots of cooling anyway to be comfortable, and I am afraid that replacing the old AC with a "same-sized" new one would likely provide only marginal improvement (if that). If I am taking the time/trouble/expense to do this upgrade I want to be happy when I'm finished.

What do the great minds here on RVforum.net think?

 

[Arch Hoagland]

Have you cleaned the cooling fins that are up on the roof? 

You have to remove the shroud and you will see them.  You can buy air conditioner cleaning spray at Walmart.

Have you removed the filter and cleaned it? 

 

[dufferDave]

Yes to both

 

[Arch Hoagland]

Hmmm sounds like a new air conditioner is in the future. Think I'd go for the 15,000 BTU. 

I was plugged into a 30 amp outlet next to my house for several years and it would run one air conditioner great so I think you'll be OK. 

 

[John From Detroit]

Most rooftop A/Cs are either 13,500 or 15000  There are some smaller ones but most are 13.5 or 15K.

Strange thing when I got mu 2005 MH it came with a pair of Carrier Air V's.  13,500 BTUs' and 13.5 amp power draw.

The first to go was replaced with a 15,000 BTU Advent air and an adapt-a-kit (uses original Carrier controls) Since the company (Carrier) stopped making RV A/Cs.

IT too draws 13.5 amps running.. a bit harder starting but 13.5 Running

The 2nd one was replaced (when it died) by a Coleman.. also 15000 and 13.9 Amps.

THe moral.. You might be able to upgrade cooling without increasing electrical draw. or even reducing it.

Edit: Removed political comment

 

[Gary RV_Wizard]

Roof a/c units are usually 15k btu or 13.5k btu and roof heat pumps are 13.5k btu.  Much smaller rigs may have an 11k or even a 7k, but not your 31 footer.  Odds are you already have the max size available, but get the a/c model number to be sure. If you already have 13-15k, then the only significant improvement would be to add another a/c.

The biggest roof a/c still runs on about 12 amps, so one a/c is ok on either 30A or 50A. The only difference is what else can run at the same time

 

[xrated]

Roof a/c units are usually 15k btu or 13.5k btu and roof heat pumps are 13.5k btu.  Much smaller rigs may have an 11k or even a 7k, but not your 31 footer.  Odds are you already have the max size available, but get the a/c model number to be sure. If you already have 13-15k, then the only significant improvement would be to add another a/c.

The biggest roof a/c still runs on about 12 amps, so one a/c is ok on either 30A or 50A. The only difference is what else can run at the same time

One of my rooftop units is a 15K BTU Heat Pump, so they do make them bigger than 13.5K

 

[dufferDave]

And right there is the $64 question--

....... the only significant improvement would be to add another a/c.

Well, there are several factors at play here, as I learned today.

First, the first commercial electrician I hired to install my 30A power outlet apparently did it wrong. The nice people at the RV repair place asked questions, shaking their heads all the while, told me he screwed up, that the screwup was why the AC was not working, and finally told me to get the outlet re-installed. That's on the schedule for Tuesday (with a new electrician who sounds like he knows the difference)

Second, the RV repair guys got the existing AC running (after fixing some burned-out system components) and showed me, but it still does not run super great. (Hey, it's 16-17 years old.) We get pretty good airflow into the front of the house but not so much into the rear (where the bedroom is). So I am still wondering if I should add a new AC and direct it completely into the rear. This would avoid any overload on the existing roof ducting. But if I do this, am I gonna need to change to a 50A shore cord, and power outlet? How much of the rest of the RV electrical system needs to change? (controls? batteries? what else?)

Last, if I add a second AC and spend all this money, am I even going to achieve the super-cooling that will make Her Majesty happy? She likes the temp in our residence at 70 or cooler, even when it's 100+ outside in Texas. If one RV AC can drop the temps maybe 20 degrees, what will the second AC do for us?

 

[Ernie n Tara]

We've found that two AC's will easily keep the temperatures in the low go mid  70's both in TX and SW FL for our mh. In fact, we run the br AC during the day at 72 F and it runs nearly full time. The lr AC then runs often when the temps get to the mid 90's. At night we reverse the operation and run the lr AC at 65 F and it pretty well cools the br by itself.

Adding an AC may be best handled by using the pedestal 20 A plug via a separate cord. Another approach, if you're qualified to work with ac circuits, is use the 50A plug to run the existing 30A load center with one phase and dedicate the second phase to the new AC.

Ernie

 

[dufferDave]

Hey, that's an EXCELLENT idea!

Adding an AC may be best handled by using the pedestal 20 A plug via a separate cord.

That would have never occurred to me. By pedestal 20A plug, I am guessing you mean that the hookups at RV parks have a second electrical hookup besides the 30A or 50A primary hookup. It makes a lot of sense to put the new AC on a separate plug.

Thanks for the help!

 

[Lou Schneider]

Last, if I add a second AC and spend all this money, am I even going to achieve the super-cooling that will make Her Majesty happy? She likes the temp in our residence at 70 or cooler, even when it's 100+ outside in Texas. If one RV AC can drop the temps maybe 20 degrees, what will the second AC do for us?

An RV will never be as cool as a house in 100+ degree heat.  Yes, the air inside may be 70 degrees or cooler with two ACs working full blast, but you'll still feel heat radiating from the windows and through the thin walls and ceiling.