High Altitude AC use causing Onan generator to die

[SFVdave]

I recently had my generator properly adjusted by a certified Onan tech. It starts and ran fantastically up to 5,000 ft. When I went up to 7,500 feet, the air conditioner wouldn't start and the generator would immediately die. Also, the microwave failed to start with the generator dying. The altitude adjustment was turned to the highest level and the generator showed trouble code 36. It was also 85-90 degrees at 7,500 feet. Everything worked fine once we left the high altitude. We have an upcoming trip to the Grand Canyon south rim which is 7,000 and may also be warm.
In reading online, I see that there is a drop of 3% per 1,000 feet rise above sea level and generator capacity drops along with some for heat. This was probably the reason for the generator dying upon start up of appliances because of spiking amperage. I tried flipping all the circuits off except those needed for the generator and the appliance, but it still failed to start.
Question, would a soft start installed on the roof AC correct the issue or will it still cause the generator to die? Microwave isn't an issue as I can run it off thge 2000 watt inverter I have.

[SFVdave]

Took a closer look at the carb and found the altitude scale goes from 0 to 6,500 feet and that should have been close enough for it to not die at 7,500 feet. I also noticed that the altitude knob doesn't stay at the 6,500 feet mark but springs back to between the 3,250 and 6,500. So that means that the altitude knob is adjusting for a richer mixture for 4,875 feet and not 6,500 feet. That's a difference of 1625 feet and another 1,000 feet higher which I was camping at totals 2.675 feet. I think that's where my problem lies. Since this generator is California compliant I will stop there,. But I believe I found the solution.

[lostbytes]

pianotuna wrote:

SFVdave wrote:
The generator is a 4000 watt installed in MH

It may require a different "jet" to work at higher altitudes.

Not knowing if that can be done with all generators. Mine sent me an 6000 feet main jet if genny being used above that. I had to contact manufacturer to get it.

[SFVdave]

Looking at option of removing the altitude dial which limits turning and to 5000 feet. If I can turn it a bit more may do the trick. I know it's not recommended.

[TurnThePage]

If your built in generator is genuinely running properly, I would try the following in order:
1. MicroAir Easy Start (or at least a hard start capacitor)
2. Shut off all other loads including the converter
3. Purchase a larger gen for high altitude trips (There's lots of good deals for Chinese ones out there.)

[3_tons]

Per the law of Occam’s Razor I would punt for a properly sized generator - per your situation, this is the right tool from your toolbox…

3 tons

[mr_andyj]

4,000 watts times 0.775 is 3,100 watts at 7500 feet elevation.

RV Roof Top Air Conditioners Watts Required for start u____Average wattage once running
7000 btu RV air conditioner 1700 ________________________600
10,000 btu RV air conditioner 2000________________________700
13,500 btu RV air conditioner 2750_______________________ 1250
15,000 btu RV air conditioner 3500_______________________ 1500

from https://www.ramsond.com/wattage-chart/

So, if you have a 15,000 BTU AC then at 3100 watts you are 400 watts shy.
If you have 13.5 then you should have plenty if running ONLY the AC.
10 and 7 btu no problem. You obviously dont have these.

This chart assumes an average inefficient RV AC unit like dometic or coleman or similar.

I suspect a carb issue and that your motor, as a result, is not able to run at peak power.

My gen runs at about 42-50% capacity when AC is running (if at 7500 feet). Yours is needing most of its capacity to just keep the AC going.

[Grit_dog]

Look into leaning it out more. Dunno what model yo have, but some (all?) have an altitude adjustment screw.
However, it would have to be running VERY poorly, very rich to not have enough snort to at least run the microwave, even if it's a little 2500W unit.
Check spark plug. If it's fouled and or dark/black then it's running rich. Insulator ideally should be a cardboard brown color. White = lean, black = rich.

Air cleaner presumably is clean since you just had it serviced, but running no air cleaner could help diagnose, it might get a "little" more air, not significant though.

Fuel, if it's fresh shouldn't matter. Octane requirement goes down as altitude goes up. Guessing it's gasoline though since you didn't specify, but you said it's in a moho.
Possible carb plugged?


And if it's LP? I'm not familiar, but presume they have an alt adj as well?

[rwynkoop]

I can second the easy start option. My 13,000 BTU AC can now be started with my 3000 watt generator when in ECO mode. In the past I had to run in normal mode.

If your generator is having problem handling the load, easy start may be the way to go. Even though it is expensive it works well.

MicroAir Easy Start - for about $330.00

Also, check this video of someone who also had a problem with their generator shutting down, even after a few ONAN techs worked on it.

Nomadic Fanatic - Fixed my generator - YouTube.

Robert Wynkoop

[valhalla360]

Did the Onan certified tech do the adjustment correctly?

Assuming we are talking about a single air/con unit on a 4000w generator, it should be OK even at altitude. My best guess is the tech didn't do the adjustment correctly.

One simple trick you can try is to turn on the fan mode, let it settle in for a minute, then flip it over to the air/con mode. This way you don't have both the fan motor and compressor motor surging at the same time...but this only works if you are borderline. If the microwave by itself is causing it to choke, it's probably not just close.

[garyemunson]

You can pry the little black limiter cap off the altitude adjuster to allow you to open the adjustment a little further. That will probably temporarily fix your issue. The jet that the altitude adjuster varies the size of is likely partially clogged. That (main jet) jet is right at the bottom of the float bowl and if any gas is left in the carb during storage, that is where the deposit builds up as it evaporates. Will cause low-power lean running that will stall the genny if a significant load is put on it. If that strategy gets it working OK again, plan on cleaning the carb jets once you are done using the RV. Onan discourages cleaning the carbs to sell new ones. Really are not too many "mechanics" capable of doing that anymore anyway. They are good, reliable carburetors that generally just have "dirty jet" issues. The main jet at the bottom of the float bowl is the most important and most often overlooked. Tricky to clean as the fuel supply enters it sideways from the altitude adjuster screw. A good overnight soak of the metal parts in lacquer thinner and "rodding out" of the passages with a broom straw (DO NOT use anything metal or you WILL be buying a new carb!!) will do the trick.

[JoeH]

wa8yxm wrote:
My ONAN had an altitude adjustment on, I think, the side of the Carb or near the carb... You may need to increase it Per page 11 of my owner's manual not all ONAN's have them.

My old Onan had an altitude adjustment lever on it too

[wa8yxm]

My ONAN had an altitude adjustment on, I think, the side of the Carb or near the carb... You may need to increase it Per page 11 of my owner's manual not all ONAN's have them.

[1320Fastback]

Does your gen have a "Altitude Adjustment" cap on the carburetor? If so ard you willing pry if off by getting a small screw driver behind it. These Gens run very lean to meet the California EPA standards when they were sold new. The cap is on the Main Jet and with the cap removed you can dial the jet richer or leaner beyond what the factory handicapped you too. The stock setting is 1.5 turns out from seated. My 4000 Microqiet at sea level purrs like a kitten at just under 2 turns out. Being at altitude you will have to be much leaner and with the decrease of oxygen you will be making less power too just like your engine in the RV.

[wopachop]

mr_andyj wrote:
Again, aside from installing a turbo charger or a super charger there is nothing you can do about the air.

Lots of campers have compressed air. How rad would the story be if someone says at 7500' and 85F they removed the air filter and shot compressed air down the intake to fire up the AC unit? 12v computer fan might act like an electric supercharger.