Generator Shuts Down On Roof Air Startup

Started by John, July 31, 2022, 04:21 PM

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1989 Chieftain. Well the title says it all, I guess. When I start the generator, the /ac fan comes on ok but when I switch to "Max AC", the generator shuts down. Any ideas?


Well, If you have the original generator and airconditioner the systems should be compatible with each other.

So first check if above is the case. IF one of the two appliances are changed out it can be that the (newer) airconditioner takes to much power or the (newer) generator is to light.

for example: a 1000W generator will not power a 1300 watt air-conditioning. so check the powerconsumption of your AC and the powerdelivery of your generator first.

If this is OK I have the next question for you, You tell me that the generator shuts off when you switch to Max AC. Is there also a Low AC position on your AC and does the generator stay running then?

If this is the case your generator can't handle the powerconsumption of your AC when it is put on MAX at the moment and you need to service your generator.  there can be multiple things wrong with it. Sparkplug(s), timing, carburation, or wrong RPM adjustment.

There are plenty of video's and instructions to find on the internet. Put the name and type of your generator in your search engine with "dies under load". Most common issue is carburation, but as said there can be other issues.


Wow, thank you for the great reply! The generator and air conditioning unit are original to the motorhome. We have had the RV for about three years and have only made one short overnight trip with it. My wife prefers to use it as a storage area bit I am trying to at least keep the systems in some sort of operational order. I would guess that the generator has never been serviced although I have routinely checked the oil level before starting. Your suggestion of trying the AC in a lower AC setting is a great idea and I'll give it a try today.

Also, I've heard of a locked rotor (sp?) in the AC unit. Maybe this could be the culprit.



Hi John,

Your welcome.

I don't think you have a stuck rotor, You told yourself the fan works fine. the fan for the ventilation inside as the fan for the condenser are driven by the same motor as shown here.

Why you first make sure electrical appliances are not connected to a power outlet  ;)

What you also can do, Connect the RV on a power outlet of your house and turn on the AC, if it works fine then you'll at least know your AC is OK. When you blow the breaker in the powerstation of the RV (normally lighter then the fuses in your house) or the fuse in your house when the fuse IS lighter then the breaker, you'll know somethings up with the AC compressor which consumes the most power.

Now if the AC works fine, then you'll know to check your generator. As said, plenty of tips of video's to be found on the internet and even here on the forum thru the search engine. Just make sure you set the search filter on "entire forum" for the best result.


Well I connected the RV to shore power and the generator worked just fine although it was somewhat underpowered because of the long extension cord and 15 amp circuit. Looks like I'll be digging into the generator soon to see if I'm capable of tuning it up.

Thanks again for the help!


Eyez Open

CRC contact cleaner does a fine job of cleaning the stator and brushes, what type of gen set do you have...Most of the amperage draws on startup..Bad startup capacitors....

About 3 cans of CRC cleaner.


I had a similar problem this spring while getting the motorhome ready for our first trip. The generator (Kohler) would start right up, I could turn on several things and it would work fine. But if I tried to start the A/C, it would immediately drop it's load. The engine would continue to run, but it would not produce any power until I shut off the A/C. Ultimately, I discovered the engine governor was stuck and wouldn't allow the engine to rev up enough to handle the load from the A/C. My solution, although probably not the best, was to shut off the generator breaker so it was providing no power to the coach and rev the engine up manually. After a few tries, the generator returned to normal operation. Good thing, because the governor is buried deep in the engine block.
Rick and Tracy Ellerbeck


Well I've been messing with the roof AC/generator shutdown thing and I think I have it figured out. After the generator has been running for about two minutes, I turn on the AC fan only and let it run for about a minute. Afterwards, I can turn on the AC on "low cool" and let it run for about a minute and then I can turn the AC to "max cool" and the generator will keep running. Seems like the AC wants to be sweet talked before putting out all the way...

Eyez Open

If you have a Onan genset there is a high speed jet on the carb, first thing would be to turn in it in as in closing the jet. Count the number of 360 degree turns to close the jet that is may take 3 turns to close it.  you need to get back to your original position so count the turns.

1. Start closing the jet... at the same time feel closely for a smooth solid close, if you encounter the slightest bumpy close you probably have dirt in the jet....a quick fix that can work would be to close the screw until you get a solid close...Now a few things do not use gorilla hands when doing this you can damage the jet easily.....Second it may well plug up the jet and you will need to pull the carb and clean you just hastened that part.

That same jet, when cold open it 1/4 turn does it run smoother? if so your running lean and probably need to adjust the choke...maybe the choke and the jet might need some love.


I've installed a Hard-Start Kit on the A/C unit.

Supco spp6

When the A/C gets old it takes more power to get started.  With the Start kit, it's much easier on the generator.

Eyez Open