High Altitude AC use causing Onan generator to die

Since genny is within spec’s you might want to try avoiding ethanol blend gas (of lower btu content, but good for ethanol lobbyist)…

3 tons

Hi,

A good solution may be a load support inverter charger. Victron or Outback. Not Magnum.

If it happens again you could try removing the air filter when you go to start the AC unit. With any luck that would allow a bit more air and keep the genny from stalling out under that initial heavy load.

I hear the soft start things will help a small generator run an AC that it normally cannot run. There are capacitors that help with the surge of power needed to start the AC compressor, but Im not certain on keeping it running part...

The issue with altitude is the thin air. You might notice your vehicle loses power also, and it probably is able to adjust itself for altitude.
The solution if the soft start does not do the trick is a bigger generator.

If you are at 7500 feet then the gen is sucking in some pretty thin air. It will not have the power needed as it would at sea level, there is no carb adjustment that will give it more power. carb adjustment will only help it run properly, has nothing to do with power.
When there is less air you adj the carb to provide less gas (called leaning it out). The ratio of air to gas must remain the same no matter the elevation, so as you go up into thin air you adjust the carb to a more lean state - aka, less gas. less gas will not give more power, it only keeps the ratio correct and the engine running smooth. Automobiles are set at a 14.7 to 1 air to gas ratio. Im not sure the small engine numbers, probably similar.

I have never HAD to have AC at 7500 feet, esp at night, but I understand wanting to be cool in the day.

I think the formula is 3% for ever 1,000 ft over sea level, so at 7,500 feet this is a 22.5% drop, so multiply by 77.5% and get worse numbers.
3,500 times 0.775 = 2,712.
Congrats, your 3500 watt gen is now a 2700 watt generator!

Now if Im wrong on the math and it is from 4500 feet then 7,500 is 3,000 over 4,500 so 3% times 3 is 9%.
2,500 watt gen times 91% is suddenly 2,275 watts of running power, not 2,500 watts anymore.
3,500 drops to 3,185 and so on....

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

Maybe the proper adjustment was for 5000 ft but is insufficient for 7500 ft.

The generator is a 4000 watt installed in MH

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

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

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.

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.

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.