Discovering that your fridge isn't cooling things down properly and that only the bags of ice cubes you brought with you are keeping the box from becoming really mushy is a downer. When this happened to a friend of mine, he asked a refrigeration technician to take a look. With no time to make a permanent repair, the technician poured several glasses of warm water over the unit's expansion valve and told my friend that if he did this every other day, the fridge would probably work fine. He was right.
The technician said that although there could be other problems, moisture had probably gotten into the refrigerant, and the resulting water vapor had frozen in the expansion valve. Some smaller units have just a capillary tube that runs to the cooling plate, but most have a brass expansion valve just upstream of the cooling plate. The coolant will be warm up to the valve and will be cold on the other side. That brass valve is where the warm water should go.
This problem is most likely to occur on boats that cruise in very humid climates, such as southern Florida and the Caribbean. So if your fridge starts to act up and you want a quick (but probably temporary) fix, try pouring some warm water on the valve. There's a good chance that melting the ice in the valve will solve the problem—at least until you have time to make a permanent repair. Rod Glover