# a/c units



## Guest (Sep 24, 2006)

My uncle just updated his Airex motor home to a 75 amp service...
He wanted to run both a/c's at the same time,,, but it has a switch panel at the back og the coach,,, 2 switches... if it is up then the rear a/c runs,,, if it is down then the front a/c runs...What he wants me to do is make it where he can run both a/c's just by turning the controls on the units (bty ,, they are dumper a/c's)
Anyway i pulled the switch panel and i was amazed at how they have this wired...
I think that it would be better to pull a new line off the converter box to the rear a/c and leave the front the way it is....
Has anyone seen this prob???? also is it a good idea to pull another feed for the rear a/c???


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## hertig (Sep 25, 2006)

Re: a/c units

75 Amp service?  Where is he going to plug it in?  Usually RVs are 15/20/30 Amp single phase or 50 amp dual phase.  What was it before (I'm guessing 30 Amp or less since it was designed NOT to run both A/C at the same time)?  Is the new service single phase (2 wires plus ground) or dual phase (3 wires plus ground)?

I'd say you would not want to hard wire it to always allow both units to run.  If this was done, someone could unknowingly or forgetfully plug it into an outlet which could not power both A/C, and attempt to use them both.  This could be dangerous (to the A/C units).  Perhaps the best method would be to add in a Power Management center, but that might be pricey and/or complex.  A cheap option if it is dual phase, would be to power one A/C from one phase and the other from the other phase, so that if you were plugged into a single phase outlet, only the one A/C would work.  But then you would be stuck with only that A/C on the single phase source.

If you provide more information, we might be able to come up with other options.


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## Guest (Sep 25, 2006)

Re: a/c units

we installed a new conveter box and breaker box... it has 2 new breakers for 110 and 5 new breakers for 12 volt,,
I was thinking of putting the other a/c on a new breaker,, all by it self and then use the other breakers to split up the system from there,,
BTY it was a 30 amp before we updated it
As far as phase it now has 220 2 hots and a ground...
Most of the rv parks he goes to has this option....


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## Guest (Sep 25, 2006)

Re: a/c units

As far as the wiring i think that i will update it to ,,gonna get rid of the dual switches and wire it in the way i want it...
(control it from the a/c units,, and not the stupid front and rear switches,,,,)
I think this will work ,,,, Any ideas on this?????????
BTY i also updated his cable tv hook up ( sorry out of the context of this forum)


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## Guest (Sep 25, 2006)

Re: a/c units

oops i meant the a/c  wiring


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## TexasClodhopper (Sep 26, 2006)

Re: a/c units

I'm hoping you understand how 50amp service is supplied at RV parks....


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## hertig (Sep 26, 2006)

Re: a/c units

No (valid) RV park provides 220 volt service, and if they did, it would likely damage a RV plugged into it since most RVs are not set up to handle 220 volts.  What is supposed to be provided is 2 out of phase 110 volt circuits.  Even though there is 220 volts available across the 2 hots, the center return wire is the key.  Because the 2 110 circuits are opposite phase, the return wire for both does not have to be bigger than each hot, as the maximum current in the return is when one or the other leg is supplying 50 amps, and the other leg is supplying no current.  Otherwise, the currents, being opposite phase, cancel each other.

Keep in mind that whatever you do, it should be as 'fool proof' as possible.  Sure, you can hook it up so it works just right under 1 set of circumstances.  But what if the unit is camping at a place which does not have 50 amp service?  Will what you do still work safely and conveniantly?  How about if the person who is using the unit does not know or forgets what it is you did?  Will he be able to hurt himself or the RV?


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## Guest (Sep 26, 2006)

Re: a/c units

The one that he goes to supply a 30 amp service and a 50 amp service,,, they also supply phone and cable hook ups,, as well as a regulated water hook up (gauge is on the hookup,, And u set it as needed)
Also he is well aware of what has been done,, also the generator is still wired to supply only 30 amps,,, (no changes there)
There are adapters that u can use for 30 amp to 50 amp and such


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## Guest (Sep 26, 2006)

Re: a/c units

The origianal 30 amp plug had 1 hot lead and 1 nuetral and a ground,,,
As far as 220 i know u need 2hot leads and the ground becomes the nuetral...


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## C Nash (Sep 26, 2006)

Re: a/c units

730 are we reading your post right?  Are you going to run 220 into the rv?  The 50 amp is 220 but it seperates in the rv and only 120 is used in most.  I know some of the total electric models have som 220 appliances. if you are just wanting to be able to run both acs you can run a seperate line to one of them and plug into the extra 30 amp plug that most CG have.  I'm probably just totatly confused as to what you are doing    What is a dumper ac :question:


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## hertig (Sep 27, 2006)

Re: a/c units

Actually, no, the ground is not the neutral.  There is supposed to be a 4th wire in that connection which is the neutral.  It is insulated (unlike some ground wires) and usually is bigger than the ground (has to be the same guage as each of the 2 "hot' wires).  The ground is to ensure that there is a common base level throughout the system, and to act as a safety if a wiring problem develops.  It is NOT meant to carry current.  

Please do a bit more research and do it the standard way.  Sure you might cobble something which seems to work, until you plug into an outlet which is wired 'differently' or even, *gasp* wrong.

I just stayed at a park where they put both legs on the same lug, so the 2 legs were in phase.  Fortunately, with a SurgeGuard and a Power Management Center, it treated it as 30 amps; who knows what would have happened if I had plugged in there without these devices.

By the way, the 30 amp to 50 amp (or the inverse of that) adapter only uses one of the phases.


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## TexasClodhopper (Sep 27, 2006)

Re: a/c units



hertig, I don't think that the 'phasing' of the two 120 legs will affect anything in your RV (unless you have one of those RVs with a 220 appliance). Having said that, I agree with you that it shouldn't be that way, because I doubt the source can provide 50amp service that way. As you know, (but perhaps someone else doesn't) a MH with 50amp service is wired into two separated 120volt circuits. This allows the wiring within the MH to be 25amp wiring on both sides.

730, your posts don't fully explain what you are doing with your wiring. The fact that the rest of us here can't completely comprehend what you are doing should make you pause to consider that you might not be doing something safe. (Also, you really have to consider the next person that gets the MH!) 

Perhaps you can further explain what you are doing? We're only trying to keep you safe!


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## bazzer (Sep 27, 2006)

Re: a/c units

The wiring in our two countrys cant be that different afterall we invented it, :laugh:  :laugh: any way for 110volt you have live neutral earth, for 220volts you have 2 lives one neutral one earth,if you use the third wire as neutral instead of earth you leave yourself wide open to death,these vehcles are mainly insulated from the ground and so need to be earthed, split the supply when it comes in the vehcle, bring in two 110volt supplies or get a qualified electrical engineer to sort it. :dead:


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## Kirk (Sep 27, 2006)

Re: a/c units

730, if you do what you are talking about, you will fry the RV systems. A properly wired RV with 50A service uses a much heavier cord that has four leads and a four pin plug at the end. It must have much heavier wire, and it must have both a neutral and a ground. Before you go any farther, make sure the insurance is paid up as you are probably going to need it.


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## Guest (Sep 27, 2006)

Re: a/c units

hmmmm ,,,seems kinda funny that my 220 compressor at home has a three wire connection,,
2 hots and the third wire is nuetral ,, also my rv has a 50 amp service also 2 hots and a ground,,, three wires that's it
It has 2 main breakers each 110 and the service is split from there...
I think that i will just wire the second a/c to the other breaker and go from there...
Also i forgot that my uncles rv is updated to 50 amps   not 75 (sorry)


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## hertig (Sep 27, 2006)

Re: a/c units

Texas, you may be right that it won't affect anything in the RV, although my power control center sure didn't like it.  However, it could very well affect the power cord.  When the 2 legs are 180 degrees out of phase, the worst case scenario is if all the power is coming on one leg and none on the other.  Thus since the neutral leg is the same gauge as the hot leg, no harm, no foul.  But it the 2 hots are in phase, then you could have twice the current in the neutral as you do in each hot.  There is a good chance that this would not have a happy ending.

I thought each leg could provide 50 amps, not 25 amps.  That is what the breaker implies, since in 220 volt mode it would seem there is 50 amps out and 50 amps in.  So each breaker would allow 50 amps, or 100 amps total in 110 volt mode  

730, 220 volt appliances/devices are designed to work on 220 volts.  RVs are mostly designed to work on 110 volts.  Applying 220 volts applied to something designed for 110 volts has potential for excitement.

Bazzer, RVs need to be be grounded via the ground wire.  The neutral wire provides the return path for the 2 110 volt circuits.


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## Guest (Sep 28, 2006)

Re: a/c units

I am not going to worry about it since my rv works this way (I have a four prong plug,, And i know one is ground) 
But is all 110 ,, but thanks for all u'r help... if it burns then u and the insurance will be the first to know :laugh:


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## Guest (Sep 30, 2006)

Re: a/c units

Ok here is what i've done...
I installed a new 50 amp converter box (and hooked it up)
I ran 110 to the original breaker (20 amp) that power all the appliances and 1 a/c unit..
I ran another 110 feed to the other breaker ( that means 1 hot lead , 1 nuetral and a ground on 1 leg ,,, same for the other one)
The other breaker also has 110 ,,( also 20 amp) powering the rear a/c unit and nothing else at this time,,,
But since i have 4 more a/c power breaker s and 6 more 12 volt breakers i'm gonna split up stuff so that it won't be pulling on one breaker anymore...
BTY it works great both a/c units work and all the other appliances work great,, and the power cord isn't getting hot anymore  (like the 30 amp did)

Thanks
again
 :laugh:


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## Guest (Sep 30, 2006)

RE: a/c units

Oopps forgot i changed the shore line also...
 :laugh:


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## Guest (Sep 30, 2006)

Re: a/c units

Dumper units are a/c units that blow form the ceiling and not the floor
OOPs this a reply from about 4 or 5 forums back SORRY


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## TexasClodhopper (Oct 2, 2006)

Re: a/c units





> hertig - 9/27/2006 10:46 PM Texas, ... I thought each leg could provide 50 amps, not 25 amps. That is what the breaker implies, since in 220 volt mode it would seem there is 50 amps out and 50 amps in. ....



hertig, you are absolutely right! All the current from both 120volt legs has to pass through the neutral wire. I misspoked about the 25amp. I meant 50amp. I was blinded by the sun reflecting off of the mountain stream I was sitting at in my recliner in Maggie Valley North Carolina!


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## Guest (Oct 2, 2006)

Re: a/c units

ok here we go again,,,
I installed a new 50 amp breaker unit (12 and 120)
I used the exiting 120 feed to power the old 30 amp (original breaker)
I ran another 120 feed to another 30 amp breaker (new breaker,, per new box)
That breaker is wired (new wiring) to rear A/C...
That means 1 (3) wire romex to 1 breaker ,,(load , nuetral and ground)
A second romex cable pulled (3) wire romex  (load, nuetral and ground)
The wiring works fine and as u see i'm pulling 120 off one breaker and pulling another 120 off the other breaker (for the rear a/c) using (2) load wires (2) nuetrals and (2 grounds)
The system works great ,, nor probs ,, can run both a/c units and no more brouwnout power when the a/c units kick on....
As for the appliances they still be on 120 (still on the original 30 amp breaker)
The genset is still 30 amp (not gonna change that)
I see it as this if he has to go back to 30 amp .. then all tha original stuff (that worked on 30 amp before) Will still operate as orginal form the factory...
thanks


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## s.harrington (Oct 3, 2006)

Re: a/c units

RV 50amp service is two legs or 120 volt , one neutral and one ground.  The two hots are usually a 30amp and a 20amp.  To run both a/c units at the same time you must install 1 new 15 or 20 amp breaker to wire the second a/c unit to.  Run the wire to the old front/rear a/c switch, install a junction box in place of the switch and hook up the a/c units one to the original pwoer wire and one to the new youjust ran.  You may have to fish the wire through the cabinetry instead of the walls.  Make sure the 50 amp service has been installed correctly in your rig.  The main breaker should be a double breaker with a solid bar between the two and the box should have altenating hot bars for each breaker.


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## Guest (Oct 4, 2006)

Re: a/c units

That is what i have done ,, i ran a new wire (3 wire romex) to the ohter breaker 
the unit works fine and also i can power both a/c units at the same time...
I won't worry about the 30 amp thingy since the fact that if he has to use a 30 amp plug in then it will be like when the coach was built...
Thanks for all the input from all of u guy's

730


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## hertig (Oct 4, 2006)

Re: a/c units

s harrington, actually, I believe that both hots are actually 50 amps each for 100 amps total into the RV (see post above).  Although I do have a box which I can plug into a 30 amp and a 20 amp, and power both legs of the 50 amp shore cord.  The one time I could have used it, it did not work (the 2 legs need to be opposite phase or my power control center gets upset).


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## s.harrington (Oct 4, 2006)

Re: a/c units

Hertig,  depends on who wired the park.  Most parks today use two 50's but some of the older ones used a 30 and a 20 to give 50 amps total.  Saved them money.


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