Replacing rear 13,500btu with 15,000btu A/C?

Why don't you install a high efficiency or an atwood unit? In both cases, they consime less power than the 13.5K you are taking out, so it makes the point irrelevant...

OP,

When we were ordering our rig (way back in 2004), we have the option to upgrade the rear AC to the same 15k BTU unit as the front for not much more additional expense. I opted to pay for that upgrade for the following reason. I figured that IF we were out somewhere and the front AC failed, if the units were identical, they should be easy to swap "in the field", allowing us to keep 15k of cooling up front where it's needed most. Since the front AC gets used quite a bit more than the rear, I thought this would be a reasonable idea. In practice to even out wear between the two, where we're out during the day, we've often left the rear AC running during the day for the dogs, and set the thermostat higher on the front AC as a backup if the rear AC failed. With the ducted system, it seems to work.

Well, here we are 14 years later, going on our 15th season, both AC's still work fine. About 5 years ago I had a bad relay in the front AC, but thanks to Doug and these forums, he told me EXACTLY what part needed to be replaced. (That man has probably saved the collective membership here on RV.net tens of thousands of $$$ over the years!!! Thank you, Doug.) I did what he suggested, and it's been working fine. Even purchased a few extra relays in case the same happened again. You guessed it, they've been fine. Proof positive that if you HAVE a spare (or spare part) you won't need it! LOL

So, that apparently worked for us. Our units both have heat strips, which I prefer to heat pumps since they work in colder temps than the heat pumps do. Maybe not as efficient, but a better choice IMO if you camp in colder weather.

In a thread currently running about expected lifetime of a rooftop AC unit, it seems like newer models don't last as long. But many of those seemed to be the heat pump models. If you're using those for heating, then you're putting more wear on the compressor than the heat strip models, which don't run the compressor at all when heating, just the fan. So maybe that's one of the reasons those units are failing faster?

Anyway, we have a 50 Amp rig, and rarely connect to 30 Amp. When we do, we just run one AC.

Whatever decision you make, good luck! :)

~Rick

^^^ Which leads to "you shouldn't run (2) ACs on a 30 amp circuit".

Can you do it? Maybe on paper, sure. Should you do it? I know I wouldn't. :W

And back on topic, is a good reason to upgrade to a 15K if you're changing one out. Run (1) 15K and enjoy a little extra cooling VS the 13.5K. We currently have a dead AC and that's exactly what we intend to do. I'll switch the working 13.5K to the bedroom and install a new 15K to the living area. Can't hurt, might help.

The direction this thread went is idiotic. The OP has an RV with 50 amp service. If he uses a doggone he can most likely run 15K and 13.5K units simultaneously from a 30 amp pedestal if he runs nothing else but converter, and if you take into account the park having good power and good connections. Especially so with two new high efficiency A.C. units. The variable in my eyes would be the parks service which is usually lacking. Especially so if crowded and you happen to be on the end of a service circuit.

I have 3 15,000 BTU heat pumps on mine and I can assure you that you will not run more than one on a 30amp service. At least for no more than two minutes. BTDT....Dennis

I think it's the way dougranier presents himself which generally starts the ball rolling with people trying to prove him wrong. It's all in the attitude. When you throw something out there as "absolute" statement because you believe you are the only qualified authority and you emphasize it with CAPS followed by your resume, it presents a challenge, especially for those that might dare to disagree.

This is a discussion board, not a "go ask doug column" and all input should be welcomed without someone trying to slam it shut. There are a lot of talents here with diverse levels of experience and education.

OMG.......Does a #10 wire have more horsepower or torque?? It's absolutely ridiculous what some of you argue over. So many of you take things sooooo literally that its almost moronic. A poster comes on here and asks a simple question and before you know it, a bunch of you are trying to prove who's is bigger.

"dougrainer" has been coming on here for years offering great service info for free. He makes a basic statement and several of you run out and start dusting off your electrical books from college. Let it go. When someone asks or answers a simple/generic question, we certainly don't need a bunch of people who tell us about the one time in 1942 that what the poster said, didn't work. Use the good sense God gave you to not dissect every little thing!

RLS7201 wrote:
Never mind. Here is a chart that shows circuit breaker trip time delay. Which would support your comment for up to 125 percent over load.
Trip Time Delay Curve

So the RV can hover indefinitely at 32 to 35 amps and everything seems fine... until it is not.

I'm currently using between 3000 and 5700 watts of electricity using 3 shore power cords. None of them are operating at over 80% of their capacity. Ambient temperature last night was -27 c (-17 f).

I'm using a 50 amp break out box that has a 30 amp outlet on one leg, and twin 20 amp outlets on the other. Each circuit has its own breaker (30,20,20). I realize that is some what unbalanced.

At 5700 watts the voltage is down to 104. I should have put my autoformer into the mix. The amps number is 54.8, unevenly split over a 50 amp pedestal.

dougrainer wrote:
I am NOT suggesting anything. I never stated anything about the wire gauge of the 30 amp shore cord. What I am stating is simple. I have worked on RV's for 38 years and NEVER has a lower amp draw been suggested for a 30 amp rated system in an RV. Remember, I am old enough to have worked on RV's for almost 20 years BEFORE 50 amp was even an option or available. I have seen numerous 30 amp ends pitted and melted and that was caused by using a 30 to 15 amp adapter. NOT really low voltage, but when you adapt down and most RV'ers are pretty ignorant about adapting down and the problems that causes, the voltage does drop and the AMP draw goes up and that generates HEAT. That causes the pitting and melting of the adapter and if on a regular 30 amp shore CG plug and you do indeed draw MORE than 30 amps, which a LOT of RV'ers do, will cause the melting and pitting on the 30 amp shore cord ends. I have customers(probably thousands over the years), come into my service center and the 50 to 30 adapter is pitted and melted on the 30 amp end and rarely will I find one not damaged from running MORE amps than 30 thru that adapter. A LOT of RV'ers think that if they overload the system the breakers will protect the system. THEY DO NOT. You must have knowledge and manage your amp draw when connected to 30 amp service or when connected with a 50 to 30 dogbone if you do NOT have a onboard EMS system. Doug

If a 30 amp breaker does not trip at a continuous load over 30 amps, then what is its purpose? Why is it RATED at 30 amps?
Are not these devices there to protect those who don't know or understand electrical loads?

Never mind. Here is a chart that shows circuit breaker trip time delay. Which would support your comment for up to 125 percent over load.
Trip Time Delay Curve

And this formula also supports your comments.

Multiply the amps by the volts. In most circuits, this will be 20 x 120 = 2400 or 15 x 120 = 1800. The number resulting from this equation is the maximum wattage load you can place on the circuit before tripping the breaker.


Richard