If your boat is like my 54 #14 you will find that the voltage coming out of
the controller to the pump is indeed 12 volts. When put in a high load
situation, as with a warm load of stuff in the freezer that must have its
heat removed or a restriction in the heat exchanging water flow, the pump
will indeed blow a fuse if it is made to work too hard. Calcification/marine
growth in the refrigeration raw water circuit is the usual trouble source
for the problem you are having but any other type of restriction in the
volume of raw water would also cause the difficulties you are encountering.
Be careful with the 5 amp fuse as it is more than double the rated current
and plastic motors will burn if they get too hot.
All the best,
Joel F. Potter - Cruising Yacht Specialist, LLC
Amel's Sole Associate for the Americas
Mailing Address: 401 East Las Olas Boulevard #130-126
Fort Lauderdale, Florida 33301
Phone: (954) 462-5869