Just a little discussion on how the system works during the heat mode. When operating as an air conditioner, the system is pretty straightforward: The heat generated during compression
is transfered to the sea water in the condenser, and heat is absorbed by the refrigerant from the air passing through the air handler.
During the heat mode, however the reversing valve turns everything around: The heat generated during compression
is transfered to the air in the air handler, warming the compartment. This heat transfer also condenses the refrigerant, so what used to be the evaporator during air conditioning
, is now the condenser. The condensed refrigerant is immediately expanded in the capillary tube at the air handler, and returns to the "condensing unit" in the engine
room as a rapidly cooling
mixture of liquid and gas (although the unit is called a condensing unit, no condensing occurs there when in the heat mode). In order for the system to absorb heat from the sea water in the coiled heat exchanger
above the compressor
, the refrigerant must be colder than the sea water. And, since the refrigerant travels on the outside of the coaxial sea water tube, it is also absorbing heat from the air surrounding it.
In your case, the refrigerant is not only colder than the 55 degree sea water, but colder than 32 degrees F, hence the formation of ice. Generally, the only variable available to increase the heating
in the air handler (if the fins in the air handler are free of dust) is changing the amount of refrigerant in the system. If you add refrigerant to the system, you increase the pressure at the compressor discharge (the head
pressure) and therefore increase the temperature at which it condenses in the air handler.
Since your system is both an air conditioner and a heat pump, and since you do not want to have to change the amount of refrigerant in the system each time you shift from one to the other, it is best to use the charts
provided by the manufacurer to put the right amount of refrigerant into the unit. Although there are charts
the system in both the heat mode and the cooling
mode, the most accurate one to use is the cooling mode chart with the unit operating as an air conditioner and using the suction pressure.
I had no idea, when I started this reply, that it would run this long, but I hope it was helpful.