If the voltage is steady the fan is just an annoyance. There are no adjustments to the WFCO. The option is to replace it and quite frankly I would replace it with IOTA or Progressive Dynamics if you ever charge with a generator. Plugged in those are great and add Powermax Boondocker as another option and might be closest to a direct replacement.
WFCO fan typically comes on or shuts off based on amperage output. They are know to fail in some odd ways.
Most likely WFCO will be fine. Can always run to WalMart or autoparts store for a 10+ amp battery charger to get you through a trip. Or maybe you have one to bring along.
