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50 Amp Coach Plugged Into 30 Amp Shore Power Cord

Roof AC Units

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#1 J79Engine



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Posted 16 September 2013 - 12:58 PM

I have a 2005 Workhorse chassis, 8.1 gas 38 ft Sunvoyager.


My question: I have two roof mounted AC units one in the bed room and one out in front area. The one in the front area sometimes makes a rumbling noise like it does not want to stay running after it has been trying to cool for some hours. Then I switch to the bed room one which both have in roof vents to pipe air to the front or back but I normally do not run both at the same time if parked at the house because I think it may be too much draw for the 30 AMP line I put in at the fuse box back when I had a 5th wheel. 


So is it OK to just run both on a 30 Amp step down shore cord to reduce the run time on the AC units or are they not meant to run continuously under load?


When I rest the front AC unit for a few hours and then turn it back on it operates fine. There is also a slide inside under each unit that allows a heavy down flow of AC air or if you close that slide vent it forces the air flow to go through the ducts in the ceiling then coming out various smaller vents between the front and back of the coach. I do not know which is easier on the AC units but it seems happier when I have the slide vent open compared to making the unit send the air through the smaller vents and pipes. I installed a thirty Amp outside receptacle to plug in the 5th wheel camper years ago which goes directly to the house fuse box, maybe I should upgrade that to a 50 Amp receptacle? 


Just for information: I also put in a dump waste pipe. Piped it through the basement and "Y"d it into out main sewer pipe. The rules do not allow it but if you call it a "clean out" access then it is OK to install. Just should not leave it hooked up when not dumping or it would raise eye brows. We use it if we used the system on the way home and it is also good for winterizing the coach and dumping MH antifreeze in the Spring. We have a 20x40 driveway cement parking  area beside our house that the MH likes to sleep in when not being used.

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#2 wolfe10


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Posted 16 September 2013 - 01:52 PM

No question, two A/C's on a 30 amp circuit is very marginal.  If both happen to cycle on at the same time, I suspect it would pop the breaker, particularly if any other 120 VAC items are on such as charger.  I would not do it.


In addition to too many amps, at high amp draws, voltage drops, which increases amp load from the compressor(s). And low voltage will shorten the life of the A/C.



You can insure less voltage drop by using your 50 amp shore power cord with just a 30 male to 50 female at the outlet. The heavier the gauge wire, the less the voltage drop.


I would also suggest you check voltage (any interior outlet would do) as the A/C starts up and as it runs.  You sure don't want to have an A/C running on less than  108 VAC.



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#3 kaypsmith


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Posted 16 September 2013 - 07:21 PM

Two ac's on 30 amp is certainly marginal, as Brett pointed out. Any thing on either of the circuits running at the same time probably will cause a circuit breaker, fuse, whichever you have.

When you use a 50 to 30 amp adapter, you are using a 30 amp single 110volt wire, then splitting into the equivalent of two 15 amp circuits. The two units probably will slave to work, and this causes overheating.

Replacing the 30 amp and going to 50 amp is definitely the best route. But remember that the 30 amp circuit probably is only number 10 wire size from the panel to the box. This needs to be replaced all the way to the panel with #6 wire, the ground can be #8. Be sure to inform the wire source as to what your goal is.


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