I have an onan 2800 gen that will not charge

I would not adjust it, I would say the unit has sat and carb is gummed up. Flush with sea foam and run for as long as you can under heavy load

While you didn't indicate the btus of the HVAC I assume it worked before? What you are describing sounds like the engine isn't making horsepwer. A 2800 is a small unit that a HVAC and some lights is about all it can stand. The HVAC takes about 6 x current to start it, than it does to run it. If this inrush is high and the generator engine isn't producing full HP then it will shut off and die on under frequency. I would recommend having and engine leakdown test done (not a compression test, as that doesn't tell the whole story. This will ensure all valves and rings are mechanincally in good shape, then try a basix tune up, plugs filters etc.

maybe old gas or dirty carburetor first replace the gas if nothing happen open your carb and clean the pilot of the carb its one small screw w/holes inside most times get clog

You need to make sure you have voltage from the stator windings, this feeds abck to the control board. Have the rotor and stator checked, and brushes and skip rings

More likely the switch is bad, and only make run contact when in the start position.
Easy to test the switch continuity with a ohm meter when it is not running.

recheck, reclean,and rebuild carb possible had moisture in fuel and carb --white smoke--but sounds like float and carb still gummed up

Possible low oil / low oil switch

Governor is out of adjustment

Altitude settings are incorrect

Idle control circuit

What is the model? Chances are the carb needs cleaning or replaced.

If the fuel filter is good and lines are good then it sounds like the fuel is making its way to the carb built trash is stopping the fuel from getting into the engine in order to run. Clean out the carb bowl and clean out the valve stem. I know on the Honda unit the valve stem is removed with the carb bowl then then with a striaght screw driver you can remove the Body once you drop the bowl down with the stem so to clean out the cyclinderical body. Good luck

The gen. is not the problem, the engine start circuit is not functioning. You need to look at the starter solenoid and starter.

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