A fan at the electric distribution center

Markitect

Quick question:
I plugged my trailer into a 20a circuit, using an adapter for the 30a plug for the trailer.
We hear the hum of a fan coming from the electrical distribution panel.
We've never heard this fan before,  even when connected to shore power, (though it's been a 30a service).
It's not particularly warm in the trailer...

We have the WFCO ULTRA III, WF-89 series 

Any thoughts?
Should we be worried?

Thanks in advance!

4ncar

It is normal. The converters fan will kick on when it senses a heavy load. This could be a draw or a charge load.