The fancy-schmancy electronically controlled fridge in the kitchen probably looked at the incoming power with the voltage was a hair high and the frequency at 63 - 65 Hz because the generator was unloaded, and said "Uh uh, No way. Bad power, Not starting."

The old fashioned mechanical stat fridge in the garage/shop don't care - if it's close, it'll go.

The same thing happens in commercial buildings - they spend big bucks putting the building on a generator, then some of the equipment has a "Clean Power Sensor" and doesn't want to run on it.

Or they connect (bond) the ground to Neutral out in the Genny trailer, and just as they're getting everything in the building started back up the ground loop trips off the GFCI Building Main Breaker because it sees circulating current on the Neutral and Ground.

Hint: You can't do that. Have to hook the Genny up as floating neutral and have the bond where the building GFCI Main expects to see it.

And this was Aggreko and a high-buck Contracting Company hooking it up. And they aren't going to listen to some Bubba off the street - or they'll steal credit for the fix...

Put some load on your generator and look at the frequency again.

-- Bruce --