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Old 05-28-2020, 05:39 PM   #1
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THOR #18972
Connecting Both A/C units to run at same time

I have a 37 ft 94 Dutchmen with 30 amp electrical service that is factory equipped with 2 Coleman RVP 7000 rooftop A/C units. In the back room, there is a switch to run either the front or the rear, but not both.

I am going on the presumption that this is to avoid electrical overload.
Now I know there are newer more efficient units that state 2 can be run simultaneously.

My question is this: Can the OEM units be connected to run simultaneously and the coach builder only separated them to be cautious, or can I bypass the switch and run them both?

This would be mostly for night time sleeping. The RV doesn't really cool down much in summer with just one. I understand that this would limit what else can run at the time but given that the old tube tv's have been replaced with flat screens etc, can it accommodate?

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Old 05-28-2020, 05:59 PM   #2
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On all of my motorhomes the AC units could be run at the same time and often did. The last 2 unfits had individual thermostats for each AC unit but the duct work was attached, meaning if the front AC was running air would flow to the bedroom through the ducts. On the current coach with the Vega Touch electronic system there is one control for both units but there are multiple temperature sensors positioned throughout the coach. Both units can and often do run at the same time.
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Old 05-28-2020, 06:14 PM   #3
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And you have 30 amp service or 50 amp? This is where I get concerned
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Old 05-28-2020, 06:43 PM   #4
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7000 series doesn't mean a whole lot.

Unless they are both 13.5 KBTU or less there is no chance or running them together on a 30 amp coach.

You could run a separate power cord for one of the Air Conditioners and plug it into the 20 Amp connection at the power pole.
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Old 05-28-2020, 07:44 PM   #5
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His rig is a 1994...
We don't know the power consumption of those older A/C units.
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Old 05-28-2020, 08:19 PM   #6
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The Coleman RVP 7000 series are 13,500 btu. You can not operate both on 30 amp service. That is why you have a choice of front or back a/c but not both.
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Old 05-28-2020, 09:48 PM   #7
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What was confusing me is that with the switch turned to rear BOTH a/c units work WHEN ON GENERATOR. Then I did the math. My 5000 watt generator is capable of near 42 amps. ( 5000 watts ÷120 volts. ) It has 2, 120 volt outputs one 30 amp output goes to the main input and second 20 amp output, to the second air conditioner.

On 30 amp shore power 2 a/c exceeds that draw.

16ACE27 good idea on the second line to the 20 amp shore power

Bob Denman the old Colemans draw 23 amps to start 10.4amps running. The math explains it. I could "technically" get them working but the minute one fires up and the other is running it would draw 33.4 amps and POP GOES THE BREAKER!

Thanks everyone for the help. I guess I will deal with this for another year or so then upgrade!
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Old 06-24-2020, 03:11 PM   #8
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Followup to the last question

I did confirm that BOTH will work at the same time with my generator.
I don't have a transfer switch, To run on generator I must plug my shore power cable into a TT30R outlet which is where my generator terminates.

So then when I run off of the generator, I can run both. If I unplug & run on shore power only ONE turns on, the other does nothing.

Since the wiring in the RV is the same for both applications why doesn't it blow the circuit breaker? How does it KNOW it's not generator?

Would someone happen to have a Four Winds/ Thor 30amp schematic?
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Old 06-24-2020, 03:53 PM   #9
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A 30amp breaker is well designed and capable of powering BOTH roof a/c units at the same time, since they are both 13.5kw capacity, or similar. Originally, though, manufacturers built in the 'dummy' switch so that owners didn't automatically assume that both would run on 30amp service, even though they CAN, with a little electrical 'management' while doing so - meaning that you must be cautious and make sure to limit other loads, such as battery charger/converter, electric water heater, and the use of certain 'high-amp' appliances, like the microwave and usage of a hair dryer, electric fryer, etc.

I have seen some models of 30amp coaches with two a/c units on the roof that do NOT have a 'either' switch - but they came later and are more recent than many current owners have.

If you are determined to run both, then you basically have to defeat/work around the installed switch that keeps from operating both at the same time, while on Shore Power. Apparently the switch is smart enough to know which 'type' of electrical service you are on, since they will both run together while on the generator.
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Old 06-24-2020, 05:00 PM   #10
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Quote:
Originally Posted by Cabreco View Post
Followup to the last question

I did confirm that BOTH will work at the same time with my generator.
I don't have a transfer switch, To run on generator I must plug my shore power cable into a TT30R outlet which is where my generator terminates.

So then when I run off of the generator, I can run both. If I unplug & run on shore power only ONE turns on, the other does nothing.

Since the wiring in the RV is the same for both applications why doesn't it blow the circuit breaker? How does it KNOW it's not generator?

Would someone happen to have a Four Winds/ Thor 30amp schematic?

I’m not familiar with your motorhome, but the generator itself is a bigger mystery than running 2 air conditioners on 30-Amp service. It is definitely not the typical 4,000-Watt Onan we see today on 30-Amp motorhomes.

I think you answered your own question on previous post when you stated the generator had separate 30A and 20A outputs. When you manually plug the 30-Amp shore line into the pedestal, the 20A that feeds the second A/C probably isn’t “plugged” or connected into anything other than a generator that’s not running.


Quote:
Originally Posted by Cabreco View Post
What was confusing me is that with the switch turned to rear BOTH a/c units work WHEN ON GENERATOR. Then I did the math. My 5000 watt generator is capable of near 42 amps. ( 5000 watts ÷120 volts. ) It has 2, 120 volt outputs one 30 amp output goes to the main input and second 20 amp output, to the second air conditioner.

On 30 amp shore power 2 a/c exceeds that draw.

......cut.....

My son’s motorhome has an old Honda 6,000 that has separate 30A and 20A circuits, and was originally a 30-Amp motorhome before previous owner upgraded to 50A. It also has 2 air conditioners now, although I’m not sure if both were original.

Anyway, can you share more information on generator? I like learning about older motorhomes.
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Old 06-26-2020, 12:11 AM   #11
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Chance,
Then if what you surmise is true then one of the a/c units must be hardwired DIRECTLY to the 20 amp line of the generator and not through the pigtail of the 30 amp.

Hmm that said then one a/c unit should run standalone if I fire up the generator and don’t plug in the 30amp line. The switch probably just toggles the 30 amp service when plugged into shore power.

I’m going to have to test that theory.
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Old 06-26-2020, 12:22 AM   #12
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Quote:
Originally Posted by Chance View Post
Anyway, can you share more information on generator? I like learning about older motorhomes.
My generator is a gasoline Onan Marquis 5000 made by Cummings.
5 KW.
AC VOLTS: 120
AMPS: 41.7
HZ: 60RPM: 1800
BAT: 12V
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Old 06-26-2020, 12:23 AM   #13
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Quote:
Originally Posted by Cabreco View Post
Followup to the last question

I did confirm that BOTH will work at the same time with my generator.
I don't have a transfer switch, To run on generator I must plug my shore power cable into a TT30R outlet which is where my generator terminates.

So then when I run off of the generator, I can run both. If I unplug & run on shore power only ONE turns on, the other does nothing.

Since the wiring in the RV is the same for both applications why doesn't it blow the circuit breaker? How does it KNOW it's not generator?

Would someone happen to have a Four Winds/ Thor 30 amp schematic?
You generator has TWO 30 amp legs. Maybe a 30 and a 20. 1 for the RV and 1 for the 2nd AC. That's how they make it work. I do not know the wiring involved to do this but I have learned this from this forum. When on shore power you could run an extension cord to the 20 amp outlet on the ped for the 2nd A/C and they both will run. A good electrician should have no problem doing that.
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Old 06-26-2020, 12:36 AM   #14
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It could be as simple as an interlock relay that energizes directly from the generator output that allows both Air Conditioners to run from the generator.

Here's an experiment:

With the generator running but the SP cable NOT plugged into either the generator output or SP can either A/C run?

Same as above but plug the SP cable into a 30 Amp SP connection with the generator running. Can you run both A/Cs in this configuration?
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Old 06-26-2020, 04:40 PM   #15
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Quote:
Originally Posted by cavie View Post
You generator has TWO 30 amp legs. Maybe a 30 and a 20. 1 for the RV and 1 for the 2nd AC. That's how they make it work. I do not know the wiring involved to do this but I have learned this from this forum. When on shore power you could run an extension cord to the 20 amp outlet on the ped for the 2nd A/C and they both will run. A good electrician should have no problem doing that.
Quote:
Originally Posted by 16ACE27 View Post
It could be as simple as an interlock relay that energizes directly from the generator output that allows both Air Conditioners to run from the generator.

Here's an experiment:

With the generator running but the SP cable NOT plugged into either the generator output or SP can either A/C run?

Same as above but plug the SP cable into a 30 Amp SP connection with the generator running. Can you run both A/Cs in this configuration?

OK NOW we're getting somewhere
cavie, yes you are correct there is a 20amp fuse & a 30 amp fuse on the generator and it appears you hit the nail on the head.
16ACE27 I tried your experiment.
With the generator running but the SP cable NOT plugged into either the generator output or SP and the switch turned to front the front A/C unit worked the rear did not.
With the generator running but the SP cable plugged into the SP, BOTH a/c units worked.

So apparently what cavie said is correct. The 20 amp leg of my generator powers the front ac ONLY.

So I should be able to disconnect that leg by the generator and install a 20 amp female receptacle (similar to what my 30 amp shore power setup is) and just have the option of plugging the front A/C unit either into SP or the generator. or I could add an automatic transfer switch.

The switch that I have in the back bedroom (see pix) appears to redirect the 30 amp a/c power circuit to either the front or the back.
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Old 07-14-2020, 07:15 PM   #16
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Ok so i found this article online which appeared to fit my configuration.
Rear A/C unit can be run on separate 20 amp shore power circuit – 1999 Southwind 35S

Since I am also replacing the 26 year old carpeting, I took up the sofa & found the junction box (see Pix) where the generator legs feed the rear A/C with 20 amp an the distribution panel with 30 amp.

I did my testing, disconnected the 14 gauge leads, did not plug the shore power cable into the generator outlet, fired up the Generator and no power to a/c.

So now I will split that circuit into a 20amp 125 twist lock, the 20 amp generator lead to a 20 amp 125 twist lock and create a 2nd shore power cable exclusively for the rear A/C. This way if I plug in either the Generator or the shore power
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Old 07-24-2020, 12:35 AM   #17
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Ok so today i finished up the wiring using the Southwind schematic I found online. It was actually pretty simple. I didn't have to pull up the sofa, I only did because I'm also replacing the carpeting.

I just wired the 20 amp RV wiring to a 12/3 Romex then to a female Nema L5-20P twist socket. And the 20 amp line from the generator to a Nema L5-20R making a pigtail I made from 15" length of 10/3 extension chord I bought at Harbor freight.

The Shore power cable was made with 50' of the remaining 10/3 extension chord, replacing the female end with a Nema L5-20R. Total cost $136.68 (100.73 for the 100" 10/3 extension chord) Harbor Freight
(35.95 for 2 Nema L5-20R & 1 female Nema L5-20P twist socket) Ebay.

WORKS PERFECT!

Thanks everyone for your input!
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