Been there done that:
Lots of "soft start", most work...for a while, then you go into a 'chase mode' to find that does, maybe you do maybe not, but either way, you chase it like that cute blonde in your math class in high school.
Then due to a major backup on I 35, my GPS gave me another way home. I take the exit and go I drive short ways and to my right is a manufacturing company. Coleman Industries AC Division IIRC. Not open to the public, so I sit in the parking lot and find a number for them. I end up talking to an in-house engineer about my problem.
Why do you need a soft start? Your unit is wearing (most likely the compressor) and as it wears it gets harder and harder to start till it won't anymore. Simple as that!
Ok, now I have the answer as to why it will start on plug-in electric but no longer the Onan.
But I am a retired engineer and this ate at me. My Ac unit worked great, but only if plugged in.
Then one hot summer night about 3 am I said Ah-Ha and I headed out to the barn and did this:
1) Unplugged and flipped the switch on my AF 1150 to the battery. Turned on my AC unit and it fired right up, blew cold like it always did.
2) Fired up my Onan and flipped the switch over to Gen power...AC still blowing cold air.
3) Did a few things from our trip that past weekend and flipped it over on external power.
Not sure how long that will last, but so far it's been over 2 years.
Don
Texas
US Army (RET)
'15 F350 4x4, CC, LWB, DRW, King Ranch
2008 Arctic Fox 1150 TC
Vietnam Combat Veteran