The aluminum evaporators over time will corrode from the inside out or
the outside in. Aluminum evaporator repairs rarely last over a month. I
have tried the special repair materials and solders with no success, so
a replacement is the only answer. The question is do you replace the
evaporator or the complete unit? The exterior skin of these evaporators
is about the same as an aluminum drink can and it resists corrosion
only because they are painted or powder coated. Nicks, scratches or a
poor coating exposes the aluminum to the moist marine environment.
Exterior corrosion is easy to spot because the coating around the
exposed aluminum will blister. Interior corrosion is a result of poor
dehydration during manufacture and lack of filter dryer capacity. There
is a good chance that moisture can enter the system any time it is
serviced in the field. Refrigerant itself will not cause corrosion but
add oxygen from moisture and combine it with oil an acid will be
formed. Interior corrosion shows up on the exterior at first as small
bubble blisters. Interior corrosion will occur on the aluminum transfer
tube welded to the evaporator. The aluminum to copper tube joint two
feet away from the evaporator is another spot where interior corrosion
develops. Separating and repairing the tube joint is almost impossible
because the capillary tube is inside the tube joint.

The first indication that an evaporator has failed is a very slow loss
of refrigerant as the first pin hole opens. If you try to patch one of
these pin holes there will be five more holes next month, the only
repair is a replacement.

Because of the changes made on the new systems like Adler Barbour Cold
Machines, where they changed the tube connections, it is expensive to
adapt them to the older units.
This is what it would take to replace your present evaporator and
return the system to a good operating condition:
1. Buy a new evaporator and have the fittings made compatible $250 plus
labor to modify tube connectors.
2. Install a new filter dryer and maybe a service fitting, connect up
and leak test, use a vacuum pump to dehydrate the system then service
it correctly. $200 to $300 unless you have equipment and know how to do
it yourself.
3. If your system uses Freon 12 the cost to service could add $50 more.

Now after this repair, there is no guarantee that the compressor or its
electrical module is going to last. These systems can last for twenty
years if they have not been opened up but once moist air gets inside
with this kind of a failure, the systems future is questionable.
Another important cost factor is there will be no warranty if things
don't work out.