Marine chilled-water AC system architecture

Chilled-water AC (Cruisair, Dometic, MarineAire) is two loops. The refrigerant loop (compressor + condenser + expansion valve + evaporator) runs at the chiller unit, usually in an engine room or utility space. It cools a closed loop of fresh water plus antifreeze via the evaporator, that "chilled water" loop is what's plumbed through the boat. Chilled water circulates at 45-55 degrees F to air handlers in each cabin, where a small fan blows cabin air across a coil. Advantages: quiet in cabins (only fan noise), efficient over long runs, one compressor serves multiple zones. Common failures: (1) Loss of chilled water pressure, check the expansion tank and air-purge the loop. (2) One cabin warm, usually a stuck 3-way valve or a failed air handler fan. (3) Chiller short-cycles, refrigerant charge issue, needs an EPA-card tech. (4) Raw-water flow to condenser insufficient, clean strainer, replace impeller, check for growth in the heat exchanger. Never charge refrigerant without proper vacuum and micron gauge, a badly-charged system will fail in a month.