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Old 07-19-2016, 04:07 PM   #1
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Can I run two A/C units on 30A service?

The coach I just bought has 30A service and two roof a/c units. I was surprised to learn that when I'm on shoreline power, I can run either the front or rear a/c unit, but not both together. Unless I run the second unit on the generator.

I actually have the owner's manual and that's what it says.

My wife, who likes it Han-Solo-carbonite-cold in the bedroom, is greatly concerned about the possible limitations to our a/c situation during our trip to Southern Utah this summer.

I read in this post that my 5.5 Onan should be able to handle both a/c units at once - although that may not apply to me since I'm wired for 30A.

However, since I can run the second a/c on the generator, that's got me thinking that I should be able to install a second shoreline receptacle and a transfer switch to provide that same power to the second a/c unit, without it having to come from the a/c. And I should be able to make the connections all in the basement (as opposed to new wiring all the way to the roof) since the a/c can already run from the generator. I kinda expect this hack has already been done before, possibly documented, possibly even on this forum? But I'm not finding that yet.

Thoughts from the gurus?
1999 Thor Four Winds Windsport M-30Q
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Old 07-19-2016, 04:27 PM   #2
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The gen should power both units at the same time which is why it as the 5500 watt gen versus a 4000. Most 30 amp units are wired to run either one while on shore power and there is usually a switch of some type to control which one. Not sure how the 30q is wired. The one I had was pre-wired for a second unit but it was not installed.
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Old 07-19-2016, 04:38 PM   #3
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Well, you are right it can be done and yes, I have done it. My old 1994 Coachmen had the same limitation. It has a switch in the rear that when lined up to the rear A/C allows the generator to run the front A/C with a separate 20 amp breaker (the main breaker is 30 amp to the house panel). I found a junction box where these two generator circuits connected to the motor home wiring and installed a manual transfer switch on the 20 amp breaker circuit. I also installed a receptacle for an extension cord (#12 wire). So I hook to shore power with the switch lined up to rear A/C, the transfer switch lined up to shore power, and plug in the extension cord to a separate 20 amp plug, which is usually present at most camp sites. This essentially turns your RV into a 50 amp service.
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Old 07-19-2016, 04:38 PM   #4
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You can add a transfer switch and separate cord but you may have to lock out the AC selector switch.

Keep in mind, you may be introducing 240 volts into your MH using 2 outlets on a pedestal, if it also has a 50 amp receptacle. Probable not a problem if done correctly.

Here is a post about doing something like it.

50A vs 30A and converting one to other.
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Old 07-19-2016, 04:39 PM   #5
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If your generator has a junction box between gen and fuse box inside you can take the 20 amp 12 gague wires out of the box and put a female plug on the gen side and male plug on fuse box side. When you want to use both airs unplug both plugs and plug a lead cord from pole to male plug. This allows both airs but only 1 will be on the 30 amp side. When done unplug lead cord and plug the 2 plugs together to run generator.
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Old 07-19-2016, 04:41 PM   #6
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Good to know I'm headed down the right path. I'm pretty handy with electrical work, so I suppose it's mostly a matter of chasing down wires.

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Old 07-19-2016, 04:42 PM   #7
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The way I did it you don't need a transfer switch. Plug and play.
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Old 07-19-2016, 04:43 PM   #8
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I am currently operating two air conditioners on a 30a circuit. I have the battery charger set to minimize its power consumption, and shut down one air conditioning unit if another large load is started.

My previous coach had a energy management system that would allow both air conditioners to operate simultaneously and automatically shed (turn off) one compressor should another large load (microwave, coffee pot , etc) be started.
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Old 07-19-2016, 04:59 PM   #9
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I have the ems. On my fleetwood. Nice system but I am stitching over to 50 amps.
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Old 07-19-2016, 06:09 PM   #10
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I've run both roof A/C's multiple times off 30 amp shore power but, always a few of them lurking, both are 13.5 K BTU and only demand 10-12 amps once past start up surge. I also shut down or limit the use of high power consuming items. Water heat goes to gas and the fridge to gas. No microwave, coffee pot, hair dryer, hot plate use when the second A/C is on.

One thing to remember concerning running the generator, camp ground quiet hours. Been to a few that flat out state no generator use which considering they had shore power available I could understand.
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Old 07-19-2016, 06:34 PM   #11
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There was a kit you could by with all you needed not sure if it is still available online or you can basically do the same ting with a 20 amp set of plugs (male on the wire feeding the a/c female on the wire to the genset) if you find the wire that feeds from the generator to the rear a/c. basically just plug it into the 20 amp circuit at the pedestal for the rear a/c. I had a Winnebago set up like this by the original owner and it worked great. Only something you should do if you understand electrical though. Do it the wrong and you got bigger problems.
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Old 07-19-2016, 10:03 PM   #12
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We just spent the last week on 30 amp and ran two out of three ac units. I did set the charge rate to 10 amps and didn't run the micro or toaster unless one of the ac units was off. I think it depends on the quality of the power also.
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