Cannot get both rooftop A/C's to operate simultaneously.

[87Itasca]

Hi all,

First of all, I just want to say that I know what I am doing is dangerous at best, and even deadly. If you do not want to chime in because of this, I understand. I will not hold any of you liable for any injury to my person, and I fully accept the liability for any injury that may occur to others.


Now, that being said...

My motorhome has two rooftop A/C units. Both of which work fairly well in their respective 'zones'. However, according to what I have read here, when my generator is running, and my shore cord is plugged into the power receptacle in the cord storage compartment, and the A/C selector switch set to 'Front', both my units should run.

Currently, my generator is inoperative, but I would like to run both units. I thought it would be as simple as wiring a Male-to Male short extension, then plugging my extension 30A cord into another 30A plug at the campsite.

So essentially I would be using two cords, my shore cord plugged into a receptacle powering the usual stuff, then an additional cord plugged into the generator/AC plug first, then into another outlet at the campsite receptacle.


I have done this, and still only have one unit operating at a time. I must be missing something here. None of my circuit breakers are tripped or off.  Both units still work fine when an individual one is selected, but both will not turn on at the same time. It is getting awfully hot here in VA, and on a 38' rig, even with the door shut between the kitchen and rear of the coach, the one unit can't keep up on 90+ degree days. If I could run both and leave the door open, it would make it a lot more tolerable in there.


Also, this would not be a permanent thing. It will only be used when it is stupidly hot, until I can get the generator pieced back together, and hopefully running.

[Jerry]

Sounds like your dealing with the same problem as me, from what I have figured out each ac unit is wired into separate breaker boxes, my rig has 2 breaker boxes and each one controls one of the ac units. I am considering changing to 1 breaker box, short of that maybe a jumper between boxes for a temp fix but I have not tried this yet, or maybe take the wire out of breaker box for the Ac and put a end on it to plug your extension cord to. I am sure none of this would be recommended but maybe it will get you by for now.

[Rickf1985]

All you are doing is feeding power into the generator from the shore power which may just burn up the generator! That plug that you plug into for generator power is power OUT from the generator! It is not power IN from anywhere. The ONLY way to get power into the RV id through that power cord, there are NO other outlets that are available to put power into the RV short of backfeeding a regular 110 outlet which would fry the breaker instantly trying to power an AC unit.

[legomybago]

You need to have 50 amp service in order to run both AC's. Sounds like you only have 30 amp

[Rickf1985]

There was someone who had wired their unit through an arduino board and had it set up so that only one AC unit would run the compressor at a time. When one compressor cycled off the other one could cycle on and vice versa This prevents an overload when only one compressor and a fan on the other are running.

[1990HR]

My HR has two AC units and only 30 amp. I have a selector switch to either turn on the back one or the front one NOT both.
I'm OK with that and would not try to change it.
Don't feel like burning the thing to the ground.

[MotorPro]

The generator has 2 output circuits . All you are doing is back feeding into the circuit that feeds the plug. (And likely killing the generator) The other circuit feeds the second air con. You could conceivably unwire from the generator and wire a second cord there but a would be really cautious.

[87Itasca]

MotorPro has the answer I was looking for. Did not realize there were two circuits. I was hoping by feeding electricity into the plug, I could defeat the need to run the gen JUST to have both A/C running. Guess not.

Guess I need to get on with fixing it then, as it is only getting hotter here. Hopefully the stator is good, as it hasn't been run in probably a good 6-7 years, perhaps more.

Mine is designed to run both in the Front position, however, only when the genset is running.

The board idea sounds interesting Rick, but I'm not well versed enough to feel like tacking all that wiring, plus the wiring on the coach.

[legomybago]

Mine is designed to run both in the Front position, however, only when the genset is running.

That's because your genny is probably a 6500 in that monster house, lots of juice. I'm really surprised that rig doesn't have a 50amp service? I thought all the big dog high-enders did Hm?

[Rickf1985]

My Pace Arrow has a 6500 and 30 amp service with two AC units. I don't know how they are set up since this is going to be a parts unit and all in it going to be torn out. I will try to pay attention to wiring and take pictures as I go.

[Jerry]

I am looking at installing a auto power selector switch for mine to prevent the back feed and redo the breaker box so it is all powered at the same time, I guess by the time it is done will actually be 50 amp service. My gen is a 8kw kohler so should have enough power for both i am not sure why it is not already set up as a 50 amp

[Rickf1985]

I doubt that it came with an 8K generator.

[TerryH]

I do believe that the generator options offered were 4Kw, 6Kw, or 6.5Kw, depending on the coach manufacturer. 8Kw and above would generally be for marine use.

[Rickf1985]

8K is far above 50 amp and probably set up for 220. It probably came out of a bigger RV at one time. Can't hurt to have it other than it is going to use a LOT more gasoline than a smaller one. They are pretty consistent on gas use, about 1/2 gallon per hour per 5K of power. So you will be closer to a gallon an hour, an all day run for the AC will cost you 10-12 gallons of gas!

[Jerry]

The best I can tell my gen uses about 3/4 gallon an hour! unless i am running ac I use baterys or a honda 2000 hope to have solar sometime in the next year before we go full time!

[Rickf1985]

That sounds just about dead on.

[Jerry]

I got to looking at my gen and it is not a 8kw it's a 7 I hadn't ever checked that just took the word of the guy I bought it from and it is only 120 volt which now I am kinda confused because it has 4 wires coming out of the head feeding power to the home I assume that is 2 wires to the breaker box and 2 to the receptacle on the back will have to do some investigating unless someone knows how it is wired.

[Rickf1985]

You should have three wires for 120 volt, Hot (black) neutral (white) and ground ( green or bare copper). It is especially important to have all three hooked up at every power point in the system on a mobile application.

[Jerry]

Thats what I was expecting to see but there is 4 black wires, guess it's gona be like many things on this rig someone went stupid on it! It looks like the gen set pretty much has to be removed in order to get to the head where the wires go. More fun

[Rickf1985]

If the wires are already connected to something then it should not be hard to determine what is what with the generator running and a voltmeter to test out the wires.

[tmsnyder]

If you're willing to run a 2nd 30 amp extension cord anyway, just run it directly to the A/C unit.   It might look a little clugey with the cord running up the wall and across the ceiling but at least you're not going to fry something. 


Or for a less redneck solution, open up the 'front / rear' switch box and find the wire that feeds the A/C you want to feed power separately to.   Disconnect it from the switch and wire nut your 30 amp extension cord directly to it.  That way it the cord is basically the plug for that A/C unit, just like if you wired it in at the ceiling.


I would keep both electric circuits totally separate. 


Don't do the male-male cord thing.

[HandyDan]

If you don't mind looking at a different forum, I think this will answer your question. (I have this feeling that I'm doing something that is going to cause the Mighty OZ to become irritated).
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/24041285/srt/pa/pging/1/page/1.cfm

[87Itasca]

That's what I need to do, then. If I can get my generator running, it won't be much of an issue. With it currently out of service (no spark, no idea if the stator is good), I can't run them both.

[DaveVA78Chieftain]

I have done this, and still only have one unit operating at a time. I must be missing something here. None of my circuit breakers are tripped or off.  Both units still work fine when an individual one is selected, but both will not turn on at the same time.

For reference:
Twin AC setups that have a generator (e.g. 6.5KW [50 amp]) that can power both AC's simultaneously have two separate 25 amp circuits [50 amps total].  Each circuit is feed by it's own set of separate windings.  One circuit powers all the 30 amp shore power cable circuits plus 1 AC and the other circuit powers the 2nd AC.   That 2nd circuit is only connected to that 2nd AC (via the select switch) which is why it can be used this way.  You have to tap into that 2nd circuit (not the shore power cable circuit) to use the 2nd shore power cable setup.

[87Itasca]

You got it. Never realized that earlier on.  It's got a 30A for the converter, and a 20A for the rear air unit.

I'm hoping I can figure out my fuse blowing problem with the genset first, then once it actually stays running, hopefully I can just use that and be done with it. It's pretty quiet when it runs, I was surprised. Much quieter than the one I have at my house.