I'm new to the forum and, well, fairly new to the RV world but hope someone can help me understand something. (And I've done a good bit of research via Google, but still haven't found a straight answer that I could understand. That's why I'm posting here.)First, my rig:2006 Thor Hurricane 33HOnan RV Marquis Gold 5500 generator w/about 1000 hours on itTwo 13,500 BTU air conditionersMy questions:1. Should I be able to run both air conditioners simultaneously using my generator?2. When I try to run both ACs on generator, the 20 amp breaker on the generator trips. I guess my question is, why not the 30 amp breaker on the generator? (I would think the ACs would/should be connected to the generator via the "bigger" breaker, but maybe I'm just completely backwards in that thinking.)3. If the generator has nothing drawing power (because its breaker has tripped) would it shut down "on purpose"? Mine did yesterday, about 15 minutes after the AC tripped the breaker. I'm trying to determine if this indicates a problem, a fluke, or is "working as intended".Thanks in advance for your help.Rick

We can run both A/Cs on our generator.If we trip breakers, the first thing we check is if the water heater is on electric. On 30A shore power, one A/C and the water heater will trip a breaker.On generator, two A/Cs and the water heater will trip the breaker.We also have a 5500 and two 13,500 a/cs.Ours doesn't shut itself off without a load, only a fault. Check the blinking light and refer to the manual.Best of luck solving your problem.

Twenty Amps is certainly not enough to run two 13.5 k BTU A/C units. It appears your RV is configured to run only one A/C at a time. You should have enough generator power to run both but not through the 20A breaker. Are you certain neither A/C will run with the 20A breaker off?

OK, On your type set up.The 30 amp on the Onan supplies the complete RV EXCEPT the Rear ACThe Rear AC should be connected to the 20 amp direct. Also may be connected thru a Front rear switch, but still direct to the 20 amp OnanThat is how 5500 Onans are wired on all Motorhomes. I suspect your 30 and 20 amp wires are reversed at the Genset. Not an uncommon problem, especially if any work had been done on the system. Start the Genset, turn the 30 amp breaker on the Onan OFF. If you get power to the rest of the RV your breakers are reversed. Doug

Running 2 A/Cs on 30A is marginal unless they are smaller A/Cs. Typically this is where the 5500 shines as it should have one A/C on 30A and the second A/C on the 20A CB. Check to see it there are any other loads on the 20A CB. There are a variety of reasons for the tripping CB. Dirt on areas inside and outside, weak CB, hard start capacitor failed or not installed, A/C problems and gen problems. Rigs with this gen can be set up to run only one A/C at a time when on 30A shore power, ie they may automatically switch A/Cs but only one will run at a time.

Thanks for the replies so far everyone - they've certainly helped me understand this better. Or at least I think so.dahkota - Water heater is off.dclark - Neither AC runs if EITHER generator CB is off (see my troubleshooting steps below)dougrainer - Your info was particularly useful. I did some troubleshooting and found the following:With only 20 amp generator CB off: Both AC units have no power All outlets have NO power No coach lights Slide does workWith only 30 amp generator CB off: Both AC units have no power All outlets have power No coach lights Slide does workPossibly unrelated: When one of the generator CBs is off (I forget which one) the "levels" button works and shows me tank, propane, etc levels. When the other CB is off, it doesn't. I only mention it because I wondered if power is being turned off to the thermostat (since it's in the same overall control panel) and that could be causing a problem. Again... new guy here... so might be completely off course.

A/C on generator question | Good Sam Community

CA_Traveler
Explorer III
May 29, 2016
Again you've got to fix the DC problem first, ie the light problem. Many controllers use DC including A/Cs and won't operate without DC. The outlets indicate they are now on the 30A CB as expected.

I suspect that someone has changed/modified your rig wiring/equipment beyond what you've just found. Given what you've posted it's strange that you have lights except when a gen CB is tripped. Also the gen should continue to run with CBs tripped.

Double check: The lights are OK w/o gen or shore power indicating at least some battery power, correct?

Given what you've posted I'm not surprised that you haven't gotten "straight answers".
DelawareRick
Explorer
May 29, 2016
The MH is 50 amp.

Doug - I swapped the black cables (though one was actually black/yellow, which gave me pause. I researched, then felt comfortable swapping them). I then repeated my troubleshooting:

With only 20 amp CB off:
Both AC OFF
All outlets ON
All lights OFF

With only 30 amp CB off:
Both AC OFF
All outlets OFF
All lights OFF

When I try to run both AC at the same time, the 20 amp CB trips, which is what it was doing before.

Doesn't seem like each AC has its own generator CB, unless I'm misunderstanding things. Otherwise one would work if at least one CB was on, right?
j-d
Explorer II
May 28, 2016
DelawareRick wrote:
Thanks for the replies so far everyone - they've certainly helped me understand this better. Or at least I think so.

dahkota - Water heater is off.

dclark - Neither AC runs if EITHER generator CB is off (see my troubleshooting steps below)

dougrainer - Your info was particularly useful. I did some troubleshooting and found the following:
***NOT SHOUTING, JUST WANT TO SET MY COMMENTS APART FROM YOUR TEXT***
With only 20 amp generator CB off: BUT THE 30A IS ON?
Both AC units have no power
All outlets have NO power SUGGESTS DOUG'S COMMENT OF LOADS REVERSED IS THE CORRECT ANSWER
No coach lights
Slide does work

With only 30 amp generator CB off: BUT THE 20A IS ON?
Both AC units have no power ***NO*** POWER??? YOUR FIRST STATEMENT SOUNDS LIKE BOTH WERE TRYING TO RUN ON THE 20A SIDE OF YOUR ONAN! TYPO HERE???
All outlets have power PER DOUG'S COMMENT, SEEMS MOST OF THE COACH IS CONNECTED TO THE 20A SIDE OF YOUR ONAN
No coach lights
Slide does work

Possibly unrelated: When one of the generator CBs is off (I forget which one) the "levels" button works and shows me tank, propane, etc levels. When the other CB is off, it doesn't. I only mention it because I wondered if power is being turned off to the thermostat (since it's in the same overall control panel) and that could be causing a problem. Again... new guy here... so might be completely off course.

IS THIS A 30A OR 50A? HOW MANY PRONGS ON YOUR SHORE TIE CABLE WHERE IT PLUGS IN AT THE CAMPSITE? 03 PRONGS MEANS 30A, 04 PRONGS MEANS 50A.

I'VE SEEN 30A COACHES WITH 5500 GENNYS. THE 30A SIDE OF THE GENNY TAKES OVER ALL BUT THE SECOND A/C AND THAT'S HANDLED BY THE 20A SIDE. THAT MEANS YOU CAN RUN BOTH ON GENNY BUT NOT ON 30A CAMPGROUND PEDESTAL POWER. WHICH IS WHY THERE MAY BE A FRONT/REAR SELECT SWITCH, ONLY FOR A/C.

TO RUN ON GENERATOR, DO YOU HAVE TO PLUG YOUR SHORE TIE INTO A CAMPGROUND PEDESTAL-STYLE SOCKET? I'M THINKING THAT ON CLASS A, PROBABLY NOT, YOU HAVE AN AUTOMATIC TRANSFER SWITCH. GENNY COMES ON LINE, ATS DISCONNECTS SHORE TIE CABLE AND POWERS COACH FROM GENNY. IF YOU HAVE AN ATS, AND ITS CONTROL VOLTAGE IS COMING OFF THE 20A SIDE AS DOUG SUSPECTS, YOU WOULD NEED BOTH 20 AND 30 ON TO SEE POWER THROUGHOUT THE COACH. ONLY PROBLEM, AS DOUG SAID, THE LOAD YOUR COACH DRAWS IS BEING SUPPLIED OFF THE WRONG (20A) SIDE OF YOUR ONAN.
wwest
Explorer
May 28, 2016
Those A/C's will draw about 10 amps each with the compressor running.

Startup of the compressor will require as much as 25 amps, >30 amps for a short off cycle restart of the compressor.

You genset likely can not support starting, restarting both compressors roughly simultaneously.
joebedford
Nomad II
May 28, 2016
You didn't say if your rig is 30A or 50A?? or did I miss it.

My rig is 50A and one AC is on one leg and the other is on the other leg. On shore power, 50A to each leg of course. On generator: 20A (or is it 25?) to one leg and 30A to the other. Basically enough to run the AC on the 20A but not much of anything else. I believe my converter is on the 30A leg with the other AC.
dougrainer
Nomad
May 28, 2016
Slides do NOT require 120 power/ Your Test is exactly what I stated is the problem. Your 30 and 20 amp breakers are wired backwards. The EASIEST way to fix this is---Most Motorhomes run the 120 wires from the Onan to a 4x4 or 6x6 metal junction box within a few feet of the Onan. Open the cover and you will see the 2 Black and the 2 white 120 wires as well as the ground wires. Just reverse the 2 black wires and your problem is fixed. Doug
Kayteg1
Explorer II
May 28, 2016
Sounds like somebody messed up the wiring on the coach and with generator having 2 separate circuits it is easy to get confused.
That would require higher skills than DIY.
I would suggest taking it to RV specialist.
If you want to to play with it, you will need to open electrical box, identify the wires and than we can help you makes sense out of that.
DelawareRick
Explorer
May 28, 2016
I just checked again regarding the tank level indicators. That doesn't work when either generator CB is tripped. Works fine if both breakers are on, works fine on shore power, works fine on battery.
CA_Traveler
Explorer III
May 28, 2016
Coach lights and monitor panel are 12V and run off of the battery and AC should not be a factor. Lack of 12V needs to be fixed first.
DelawareRick
Explorer
May 28, 2016
Thanks for the replies so far everyone - they've certainly helped me understand this better. Or at least I think so.

dahkota - Water heater is off.

dclark - Neither AC runs if EITHER generator CB is off (see my troubleshooting steps below)

dougrainer - Your info was particularly useful. I did some troubleshooting and found the following:

With only 20 amp generator CB off:
Both AC units have no power
All outlets have NO power
No coach lights
Slide does work

With only 30 amp generator CB off:
Both AC units have no power
All outlets have power
No coach lights
Slide does work

Possibly unrelated: When one of the generator CBs is off (I forget which one) the "levels" button works and shows me tank, propane, etc levels. When the other CB is off, it doesn't. I only mention it because I wondered if power is being turned off to the thermostat (since it's in the same overall control panel) and that could be causing a problem. Again... new guy here... so might be completely off course.

Forum Discussion

A/C on generator question

About Technical Issues

Related Content

15K BTU A/C and Generators

A/C and a generator

Generator question

Portable generators question

Generator questions