That's the same converter that I replaced. I doubt the 30A fuse was for the fan. I think it's one of two that are in the charging circuit that are supposed to prevent a reverse charging current on the battery.
I wonder if the fans stay off if you are not connected to shore power? I really didn't pay attention to the ones in mine and don't know if they were always on whenever I was plugged into shore power. They are there to control heat buildup in the charging circuitry. If they are only on when you are plugged into shore power, they won't discharge the battery, since it is being charged then. And, if this is the case, they may only be on if the battery is receiving a heavy "absorption" charge. Your battery may be in a low charge state, if the 30A fuse was blown.
However, if they run when you are disconnected from shore power, then you WOULD be discharging the battery and they should not be on then. Let me know about this, please.
And if I'm confusing you with this, let me know and I'll try to clarify.
- Jack