[Oak]

As Roland said, your compressors will pull higher amperage on startup which will cause the voltage to drop and it snowballs from there.

Get a voltmeter that records high and low and see what the voltage drops to when the refrigerator starts.

Another good test is plug a heat gun or hairdrier in it. If the gen doesn't stumble when either of those are turned on your machine may have an issue with the inrush of current at startup. There is no inrush current with a heat gun or hairdrier.

Older generators make crappy power. I wouldn't run anything with any type of electronics in it off of a non-inverter controlled machine.