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Old 05-27-2008, 10:37 AM   #1
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Pleasant Surprise with Dual A/C Units on 30 Amp Service

I have been restoring a 1984 34' Limited for the past two years. All is going well (still needs a polish). Anyway, I replaced the aging A/C unit with a 15K btu Carrier low profile last summer hoping to get better cooling. The cooling was better, but was still not adequate on this long trailer. I took the plunge this fall and installed a second 15K btu Carrier low profile in the rear bedroom (it's a mid bath unit). I had to run power and a drain hose in the interior wall, but that is no hill for a climber once you have popped as many rivets as I have.

I also upgraded the electrical service to 50 amp. I carry a 50 - 30 amp pigtail. I also made one of those dual plugs that allows you to plug a 50 amp unit into 30 and 20 amp receptacle to get enough juice to run both a/c units.

Anyway, I was VERY surprised this weekend when I pluged into a single 30 amp service and was able to run both a/c units all weekend simultaneously. It was awesome and it was cold. I was surprised that I was able to pull enough juice to get the job done, but we had no problems.

Am I missing something or can I expect to always be able to run both units off 30 amp service. Did I waste my time and money upgrading to 50 amp service in the trailer?

Anyway, I am happy with the result, which was a cold trailer on a 90 plus degree Texas afternoon. We will see how we do in July in 100 plus degrees, but I do not expect any issues. My kids were sure happy that I wasn't always ragging on them to shut the door.
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Old 05-30-2008, 03:18 PM   #2
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Pleasant Surprise with Dual A/C Units on 30 Amp Service

I have been restoring a 1984 34' limited for the last two years. I replaced the original a/c unit with a Carrier 15K btu low profile unit hoping to improve cooling. While the unit works fine, it can't keep up during the peak heat of our Texas summers.

This spring I made the plunge and installed a 2nd Carrier 15K btu low profile in the rear bedroom. I also upgraded the electrical service to 50 amps. On our first trip out, we were not going to have 50 amp service available, so I made up one of those 50 amp to dual 30/20 amp converter boxes. I was hoping to be able to run both a/c units even though 50 amp service was not available.

Well, much to my surprise, both units ran fine all weekend on a single 30 amp service. I did not think a 30 amp service would be sufficient to run them both, but it was.

Is this normal? Did I waste my time upgrading the electrical service to 50 amps?

By the way, the coach is now plenty cool. I suggest that two a/c units is a requirement on these super long trailers.

Baxter
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Old 12-05-2010, 07:51 PM   #3
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That's IT, I'm doin' it too. In the summer break in Galveston the 34' trailer would hardly pull down to 85F inside. We bought a blower to help circulate the heat from the bedroom up into the front but all that did was even out the heat problem. At night the A/C did catch up and finally kicked out at 1AM.

I suspected that a 30A hookup might be enough. Other users are creating a second land line to provide power to the second A/C, why not just go to 50A instead? If I was going to go to 50A what would I have to upgrade?

I've got a Dometic Brisk Aire 13500 BTU right now and should add a 15000 BTU to the back. Inland RV suggests attaching into the crossmembers in the roof to help support the weight and that sounds like a good structural idea. HIHOAGRV also has a good writeup about his install.
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Old 12-05-2010, 10:52 PM   #4
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I have two 13500 units in my trailer. Typically, when I measure the current draw with both running, it's 24 amps on high fan and 22 amps on low fan. With the fridge pulling around 2 amps and the converter pulling around 2 or 3 (as long as the batteries are charged) the total is barely under what a 30 amp service can provide. Since air conditioners draw more power on hot days I suppose sometimes I might go over that a little. With two 15000 units the power draw would be a little higher.

There's really no reason to put a 15000 BTU unit in the rear since even with a 13500 that will stay cold enough. It's the front that needs more cooling.
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Old 12-06-2010, 03:45 AM   #5
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Jammer,

I assume your unit has two Dometic units, rather than Carriers which are no longer sold.
Does your installation include the Energy Management System load shedding that shuts down one compressor if the load gets close to 30 amps?
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Old 12-06-2010, 04:35 AM   #6
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I also have a 34' in Texas and you are so right. One A/C is not enough. So I also installed a Carrier in the rear bath. But instead of installing 50 Amp service, I just ran a separate 20Amp line so no changes to the breaker panel. It works fine and the two A/Cs keep the Airstream comfy cool. This was one of the best upgrades I did. I also used a low-profile Carrier on the rear and planned to replace the original Dometic with a low-profile Carrier. Now, since Carrier discontinued the low-profile unit, I'll have to have mis-matched low-profile units. Oh well. Still love my Airstream.
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Old 12-06-2010, 04:37 AM   #7
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Quote:
Originally Posted by panabax View Post
I have been restoring a 1984 34' limited for the last two years. I replaced the original a/c unit with a Carrier 15K btu low profile unit hoping to improve cooling. While the unit works fine, it can't keep up during the peak heat of our Texas summers.

This spring I made the plunge and installed a 2nd Carrier 15K btu low profile in the rear bedroom. I also upgraded the electrical service to 50 amps. On our first trip out, we were not going to have 50 amp service available, so I made up one of those 50 amp to dual 30/20 amp converter boxes. I was hoping to be able to run both a/c units even though 50 amp service was not available.

Well, much to my surprise, both units ran fine all weekend on a single 30 amp service. I did not think a 30 amp service would be sufficient to run them both, but it was.

Is this normal? Did I waste my time upgrading the electrical service to 50 amps?

By the way, the coach is now plenty cool. I suggest that two a/c units is a requirement on these super long trailers.

Baxter
It's better to have two 30 amp cables instead of a 50 amp cable.

The second cable can be used for the second AC, all by itself.

Andy
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Old 12-06-2010, 07:02 AM   #8
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I would strongly suggest that you have a volt meter permanently mounted in plain sight. While you might sneak in under the limit as far as current draw will a very good service if the voltage drops below 110 on the supply side you will be doing real damage to those AC units.
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Old 12-06-2010, 07:22 AM   #9
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Originally Posted by markdoane View Post
Jammer,

I assume your unit has two Dometic units, rather than Carriers which are no longer sold.
Does your installation include the Energy Management System load shedding that shuts down one compressor if the load gets close to 30 amps?
I have two Dometic Penguins.

I do not have any kind of Energy Management System at this point. Because I stay in a campground with only 20A power for two months out of the year (see the "worst shore power ever" thread) I am tentatively planning on building a modest EMS of my own design that would do little more than make sure only one air conditioner runs at a time.

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It's better to have two 30 amp cables instead of a 50 amp cable.

The second cable can be used for the second AC, all by itself.

Andy
I'm not sure I follow. Few sites have two 30a connections on the pedestal.
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Old 12-06-2010, 07:27 AM   #10
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I'm not sure I follow. Few sites have two 30a connections on the pedestal.
Andy and I discussed this in the past. He suggested that you could use an adapter to plug one of the 30 amp lines into a 50 socked when available and the other 30 into the 30 amp socket.

I agree, I wish my Excella has a second AC. Summertime for me involves shorts, tank tops, and fans.
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Old 12-06-2010, 09:48 AM   #11
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I still don't get it.

The way my traylah is wired, when 50a is available, the rear air, microwave, and water heater go on one leg, and the converter, fridge, front air, and outlets go on the other. Each leg is 50a so there's plenty of power and I don't have to fuss around shutting off the water heater when I want to use the microwave and so on.

I have a 30a shore power cord with a 50a Marinco connector on the trailer end that I use when 50a is unavailable or unnecessary, so I don't have to use an adapter or deal with the hassle of the heavier 50a cable.

I guess I could put a 20a inlet next to the 50a one and wire up a little transfer relay for the air conditioner if I thought I wanted to run it on a separate shore circuit.
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Old 12-06-2010, 05:06 PM   #12
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We were talking about what makes more sense for a retrofit. It the trailer already has 50 amp connections, no retrofitting is necessary.

I had asked about upgrading to 50 amp wiring and connections specifically and Andy suggested that it would be simpler to leave the current 30 amp system alone and add another 30 amp service for the second AC.

I would also take the position that a 30 amp cord with a 50 amp connection for the trailer is an adapter. Just a very big one.
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Old 12-07-2010, 01:16 AM   #13
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On my unit, I have the original 30A cable, plus a 20A cable for the rear A/C only. In over twenty years of stopping at RV parks, I have never found one that offered 30A service that did not also have a separate 20A grounded outlet. Those that offer 50A service always also have a 30A and 20A receptacle.

So, no adapters and if it's not too hot, only one 30A cable, the 20A cable sits quietly in the power cable compartment.
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Old 12-07-2010, 05:53 AM   #14
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If you are shopping and looking for 30 ft. or more, I suggest you seriously consider one with dual AC. We purchased our trailer new in 2008 and two units was a must on our list. We have never looked back on our decision. We often run the rear unit when in the front during the day. I've never tried to run both on a 30 amp circuit. We usually do 50 amp during the summer and 30 amp in the winter months. We love our dual units :-)
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