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Old 07-10-2013, 07:23 PM   #1
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AC wiring

I have a 1988 HR Imperial 35 ft'er. There are 2 Coleman overhead air conditioners not connected to a thermostat. There is a selector switch under one of the closets to choose front or rear. The previous owner said there was a position for running both off the generator. Not so.

Following an older post here, my son rewired the AC' so that now I can run both off the generator, but still not off shore power. What I want is to be able to run both off shore power.

Does anyone know how to rewire the AC's so that both run at the same time on shore power? Does the selector switch have to be totally bypassed?

Thanks in advance .
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Old 07-10-2013, 07:30 PM   #2
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Anytime I hear that an owner "rewired" his coach, I get a bit nervous--is your son a qualified electrician???...Basic questions include things like the size of you generator and whether your coach is wired for 30 or 50 amp shorepower?
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Old 07-10-2013, 10:14 PM   #3
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My son is a qualified and certified electrician. My coach is 30 amp. Reading thru the manuals, my son says that the 30 amp will handle both units running, he's just not sure how the system is set up and won't go trying things for the fun of it. Like I said, we followed an old post from this site on how to change the generator set-up, but want information on changing the system so that both A/C's run on shore power. Any constructive information will be welcomed and appreciated.
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Old 07-10-2013, 10:32 PM   #4
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First you need to look at the labels on the air conditioners to see what their start and run current is. You might be getting too close to the 30 amp wiring capacity of your coach. Remember there are other things that can be running off the AC like the fridge and the battery charger. You might be able to run both air conditioners, but that's it. No TV, no microwave, no fridge, no battery charger, etc.
You can check the current draw with a clamp around amp meter and just do the math.
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Old 07-10-2013, 10:45 PM   #5
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30 amp service is not large enough to run 2 rooftop A/C's simultaneously.

That's why the original wiring has a selector switch to choose which one you want to run.

What you can do is to run a separate dedicated 12 gauge 20 amp power cable from a new box in your coach to the pedestal solely for the rear A/C. For the coach side, it would require you to run a wire from the rear A/C to the box where the 20 amp 12 gauge wire is terminated.

In the box you would need a small sub panel with a 20 amp circuit breaker solely for the A/C.

Now with that configuration, you would run your front A/C off the 30 amp coach service and the rear A/C would run off the 20 amp power cord.

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Old 07-10-2013, 11:05 PM   #6
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Quote:
Originally Posted by Dr4Film View Post
30 amp service is not large enough to run 2 rooftop A/C's simultaneously.
We run both ours at the same time on 30 amps with no trouble, but we have 13.5 heat pumps.
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Old 07-10-2013, 11:17 PM   #7
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My coach is 50 amp but my service @ home is 30 amp

I run my 2- 13.5k dometics on 30 amp all the time...without any problem

BUT...that is all that is using electric..everything else is shut off
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Old 07-10-2013, 11:35 PM   #8
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Quote:
Originally Posted by Mr_D View Post
We run both ours at the same time on 30 amps with no trouble, but we have 13.5 heat pumps.
Quote:
Originally Posted by sc3283 View Post
My coach is 50 amp but my service @ home is 30 amp

I run my 2- 13.5k dometics on 30 amp all the time...without any problem

BUT...that is all that is using electric..everything else is shut off

I have done the same with my 50 amp coach as you guys have done with your 50 amp coaches. However, the OP's coach is a 30 amp service coach with 30 amp wiring throughout.

I don't think it is the safe thing to do nor would I recommend it to anyone with 30 amp service RV's.

I had previously owned a 30 amp coach, a 1992 Airstream Landyacht that had a switch for choosing front or rear A/C's. The difference between mine and his is I had the ability to run both A/C's every time I had the generator running whereas his was not wired to do that.

I will leave it up to the OP as to what he wants to do, after all, it his coach and he can do as he wishes BUT I still would not recommend running 2 A/C's which could draw over 30 amps if the compressors were starting up at the same time.

JMHO

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Old 07-11-2013, 06:19 AM   #9
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Quote:
Originally Posted by Dr4Film View Post
I have done the same with my 50 amp coach as you guys have done with your 50 amp coaches. However, the OP's coach is a 30 amp service coach with 30 amp wiring throughout.

I don't think it is the safe thing to do nor would I recommend it to anyone with 30 amp service RV's.

I had previously owned a 30 amp coach, a 1992 Airstream Landyacht that had a switch for choosing front or rear A/C's. The difference between mine and his is I had the ability to run both A/C's every time I had the generator running whereas his was not wired to do that.

I will leave it up to the OP as to what he wants to do, after all, it his coach and he can do as he wishes BUT I still would not recommend running 2 A/C's which could draw over 30 amps if the compressors were starting up at the same time.

JMHO

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I agree^ with Richard. I have two AC's with 30 amp, but have a shed function that will shut down the second AC if insufficient power is there, and a warning light will come on indicating insufficient power.
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Old 07-11-2013, 11:49 AM   #10
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Originally Posted by Dr4Film View Post

I have done the same with my 50 amp coach as you guys have done with your 50 amp coaches. However, the OP's coach is a 30 amp service coach with 30 amp wiring throughout.

I don't think it is the safe thing to do nor would I recommend it to anyone with 30 amp service RV's.

I had previously owned a 30 amp coach, a 1992 Airstream Landyacht that had a switch for choosing front or rear A/C's. The difference between mine and his is I had the ability to run both A/C's every time I had the generator running whereas his was not wired to do that.

I will leave it up to the OP as to what he wants to do, after all, it his coach and he can do as he wishes BUT I still would not recommend running 2 A/C's which could draw over 30 amps if the compressors were starting up at the same time.

JMHO

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Here here Richard!

I would recommend setting up the second cord to the other A/C as Richard suggested in a previous post.

I have 30amp and can only run both A/C off gennie. I have never needed to run both but the gennie is set up so that the second unit runs off a separate 20 amp gennie breaker.

I would never even consider wiring both A/C on 30amp. Way too much current draw when both compressors start up.
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Old 07-11-2013, 12:36 PM   #11
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Electrical engineer here... Right off the bat as has been said, two ACs on the 30 amp is too much of a stretch. Hard to analyze in detail and say the right things without knowing AC specs and wiring diagram of what you have now. Even if two *could* run together, there'd be no room left for other loads.

I have to wonder if your 30 amp breaker would be able to handle the startup current of the 2nd AC after the 1st one is running. I am certain both would not be able to start up at the same time. You *could* consider a hard start capacitor mod. Can't this helping for two tho. Here's a good read on this anyway:

RV Air Conditioner Hard Start Capacitor | ModMyRV

As the cg voltage starts to go down, an AC will draw more current and will reach a point that two ACs would definitely not run (if they even could) on the 30 amp service and if even low enough, not even one. Low voltage is really hard on an AC unit so you need to watch what the voltage is doing. Good idea to have a line monitor plugged in or hard-wired even. Or at least use a voltmeter. At peak temp. times of the day, cg voltage can really take a dive. If down to 105 volts or less, it's time to shut down everything in your RV to prevent damage. High temp. + meal time can be a killer on cg voltage.

That's a great idea to consider using the 20 amp receptacle in the cg pedestal. You could install a Marinco or equivalent power inlet on side of your unit. You'd need to run 20 amp wire inside to a single 15 amp breaker in an enclosure somewhere, then dedicated 15 amp run from there to AC unit. In fact, this is a good idea even if you want more power for something besides an AC like say for crock pot, rice cooker, etc. so you can still run all your other regular things at the same time. The only downside on this for an AC is that to deal with low voltage, you'd need a 2nd voltage booster if you wanted to maintain 120V.

Do you really need the total BTU output or want to keep two different areas cool at the same time? What about just operating the 2nd one in the bedroom area in the evening before bedtime and have the other off?

Despite all objections, recommendations, thoughts and opinions here, if you just have to try running both units, you could think about using an autotransformer to maintain the voltage at 120V. That is, if two can even run at the same time. Franks and Hughes both make a "voltage booster" that does this. Heavy, bulky and not cheap.

A surge protector is a really good idea for protection. With low voltage, it shuts down at 102 volts (at least the Surge Guard one does).

Experts are predicting the earth will have the highest ever recorded temperature this summer. I heard on the radio recently that this will be somewhere in the US and will reach 140 deg. F or more. Can't blame some for wanting to get their ACs running at full potential. Glad we live in the PNW....
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Old 07-11-2013, 01:54 PM   #12
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Franks and Hughes both make a "voltage booster" that does this.
Frank's is junk. It comes with a sticker to not run AC & electric water heater the same time.

The new kid on the block that really works with a 12% boost not 10% is PowerMaster

A new Coleman 13.5K P.S. only uses 10.3 AMP's. I run 2 of them the same time in my MH with a Energy Management system.
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Old 07-11-2013, 02:02 PM   #13
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Some tests I have done.. I had two Carrier Air V 13,500 BTU A/C's and with nothing else on save the converter (and batteries full) and having JUST cleaned the condenser coils (outside coils) and everything else cleanable.. I ran them both on a 30 amp site and popped the clamp on around either the hot or neutral wire (Frankly don't know which)

27 amps.

Of course soon as someone else in the park turned on their AC and the voltage dropped a volt or two. CLICK and off they went.

I will leave it to MyRedRacer to explain that if he wishes. I did it elsewhere once already today.
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Old 07-11-2013, 03:20 PM   #14
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What clicked off exactly? Assuming you mean the AC units? Here's the online manual that appears to be for yours. LOTS to read in it.

www.transportaircon.carrier.com/Files/Bus/Local/US-en/T298.pdf

Says operating voltage is 115 volts. That is often the nominal operating voltage for equipment to take into account actual voltages at point of use. Nameplate amperage is 13.4 amps. Locked rotor amps (LRA) is 60 amps.

LRA is the short duration instantaneous peak current upon startup of the unit. Manual says a 20 amp breaker is needed. If you were to look at the RV main breaker size required, if looking at just two AC unit loads, you would take the full load current of 13.4 amps, add the code required 25% safety margin and add the 20 amp breaker requirement to it which is well over 30 amps. So if you are managing two AC units now, you are pushing it already. At least this is my take on it, but local codes may vary and are subject to change...

I see that the manual says there are error codes you can read. Also says that the operating voltage must be within 10% of operating voltage or it will cause premature compressor failure. 10% drop would be 90% x 115V = 103.5 volts. 105 volts is the number I usually see mentioned on RV forums.

The wiring diagram shows an overload protection element for the compressor motor. There's also a couple of thermistors in there. These both seem to be self-resetting. Sometimes overload protection on a motor requires manual resetting. Not sure on this unit, but seems self-resetting.

If your AC unit is already running in a warm/hot ambient temperature, the overload element can trip at a lower amperage. I'm guessing that as the cg voltage drops as you say, the AC units draw more current, and the overload elements, which are bimetallic strips sensitive to heat, heat up and trip. If they are self-resetting, when the overload element cools it will reset, but will cycle off again if the cg voltage is still low.

Anyhoo, without really delving into the specifics of your unit and giving myself a headache in the process, this is how I see it....
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