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 TM 55-1905-219-14-1
HEATING, VENTILATION AND AIR CONDITIONING SYSTEMS (HVAC).
a. The Air Conditioning System (Figure FO-27) consists of-a single air conditioning plant and suitable duct work
serving the Crew's Berthing, Stateroom, Pilot House and Galley Mess.
b. The Air Conditioning Plant consists of a condensing unit assembly, a heat exchanger, an air conditioning
cooling coil and a gauge board. It is located below deck at Frame 30 Starboard.
c. The Condensing Unit Assembly consists of a compressor unit, condenser unit, receiver and associated valves
and controls. This unit is designed for automatic operation to supply refrigerant to the cooling coil. The condenser has an
operating capacity of 7.8 tons and requires a refrigerant charge of approximately 70 pounds (31.8 kg).
d. The Compressor is a reciprocating type, positive displacement pump. The compressor removes refrigerant
gas from the evaporator and delivers it to the condenser under pressure. The pressure allows refrigerant heat to be
absorbed by sea water at ordinary temperatures.
e. The Condenser is a shell and sea water tube heat exchanger. It condenses the compressed refrigerant gas
and lowers the temperature by removing heat.
f. The Receiver receives liquid refrigerant that drains from the condenser. It serves as a liquid refrigerant
reservoir when there are load changes in the system, and as a storage space when pumping down the system. It also
serves as a liquid seal against the entrance of refrigerant gas into the liquid line.
g. Receivers are provided with two bull's-eye sight glasses or with a magnetic, gauge type, liquid level indicator
for the observation of liquid level in the receiver. To keep a liquid seal, there should always be a minimum liquid level in
the receiver when the system is in operation. During shutdown, the refrigerant charge is pumped into the receiver so that
only gas stays in the rest of the system.
h. The Evaporator is the part of the system where the refrigerant is vaporized to produce refrigeration. The
compressor keeps a reduced refrigerant pressure within the coils. At this reduced pressure the liquid refrigerant
evaporates or boils at a temperature low enough to absorb heat from the air, fresh water or brine in contact with the
outside of the coils.
i. The Heat Interchanger is a shell and tube heat exchanger connected in the main suction and liquid lines near
the compressor. Inside the Interchanger, the cold suction gas is used to cool the warm liquid refrigerant. This causes
greater capacity and efficiency in the system. A liquid line bypass valve is usually provided to isolate the interchanger in
case a liquid leak develops in the suction line or the compressor discharge gas temperature rises above 240F (115.6C).
1-113
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