Chapter 6REFRIGERATION AND AIR CONDITIONING
falling temperatures until the water in the system
starts to boil.
When most of the evaporated moisture has
been evacuated from the system, the indicator will
show a decrease in temperature. As soon as the
temperature reaches 35 °F (0.2 inch Hg, absolute),
admit dry air through a chemical dehydrator
into the system at a point farthest from the pump.
As the pump continues operating, the dry air will
mix with and dilute any remaining moisture.
Secure the opening which feeds the dry air to the
system. The system must continue evacuating until
the indicator again shows a temperature of 35 °F.
At this time, the dehydration process is complete.
Close the valves and disconnect the vacuum
as activated alumina and silica gel. However,
when special drying agents are employed they
should be reactivated in accordance with the
specific instructions furnished by the
After reactivation, the drying agent should be
placed back in the dehydrator shell and sealed as
quickly as possible, in order to prevent absorp-
tion of atmospheric moisture. When the drying
agent becomes fouled or saturated with lubricating
oil, it must be replaced with a fresh charge, or
with a dehydrator cartridge, taken from a sealed
Sometimes it is impossible to obtain a
temperature as low as 35 °F in the vacuum
indicator. The probable reasons for this and the
corrective procedures to take, are as follows:
1. Excess moisture is present in the system.
Because of the acid being formed, the dehydra-
tion procedure should be conducted for longer
Remember that the dehydrators that are
permanently installed in refrigeration systems of
naval ships are designed to remove only the
minute quantities of moisture unavoidably
introduced in the system. Extreme care must be
taken to prevent moisture, or moisture-laden air,
from entering the system.
CLEANING THE SYSTEM
2. Absorbed refrigerant is present in the
lubricating oil contained in the compressor
crankcase. Remove the lubricating oil from the
crankcase before proceeding with the dehydration
3. Air is leaking into the system. The leak
must be found and stopped. It will be necessary
to repeat the procedure required for detecting
leaks in the system.
4. Inefficient vacuum pump or defective
vacuum indicator. The defective unit(s) should be
repaired or replaced.
Systems may accumulate dirt and scale as a
result of improper procedures used during repair
or installation of the system. If such dirt is
excessive and a tank-type cleaner is available, con-
nect the cleaner to the compressor suction strainer.
Where such a cleaner is not available, insert a hard
wool felt filter, about 5/16 inch thick, in the suc-
tion strainer screen. The plant should then be
operated with an operator in attendance, for at
least 36 hours or until cleaned, depending upon
the size and the condition of the plant.
Immediately after each period of use, or after
the system has been opened for repairs, the dry-
ing agent in the dehydrator should be replaced.
If a replacement cartridge is not available, the dry-
ing agent can be reactivated and used until a
replacement is available.
AIR CONDITIONING CONTROL
Reactivation is accomplished by removing the
drying agent and heating it, for 12 hours, at a
temperature of 300°F to bake out the moisture.
The drying agent may be placed in an oven, or
a stream of hot air may be circulated through the
cartridge. These methods are satisfactory for reac-
tivating commonly used dehydrating agents such
Most of the information presented to this
point applies to the refrigeration side of a system,
whether it is used for a refrigeration plant or for
air conditioning. The compressor controls for
both type systems are nearly identical, however,
the devices used to control space temperatures dif-
fer. A two-position control, sometimes called the
on/off control, is used for the automatic control
of most shipboard air conditioning systems.