You did not mention if other coach loads were also being affected by this same control issue? Perhaps a second fan with the same issue?
So either the Firefly system is controlling your fan(s) motor by direct wire connection to the fan (with a small relay either located in the control pad (likely not if low profile).....or located at the fan).......or the control pad is wirelessly controlling the fan(s) which would definitely require a wireless receiver located near the fan to receive the control signals and a mini relay to connect the 12vdc to the fan when required.
If you have a second similar fan in the coach controlled wirelessly (which is working fine) you could try swapping the fan receiver modules (if they are the same module) to see if you just have a sensitive receiver module on the one problem fan.
Failing that approach, you could try to go through your AC system (safely) tightening all ground connections starting with the transfer switch (a good idea to check all connections anyway based on the poor connections discussed on this forum). Since both shore and gen cause enough AC/electrical “noise” to cause this problem the transfer switch and AC breaker panel connections are a good place to start checking for good and tight connections. I would think that the coach batteries would act like big filter capacitors to help filter any AC noise coming through the converter into the DC circuits. The converter would also have its own filter caps of course.....and the fan receiver module would use DC power for its electronics too. I would be surprised if AC power RF (through the air) harmonics are interfering with the fan wireless receiver......but you never know.
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