RJ150-30 / Operations and Maintenance Manual
Mobile Aircraft Air Conditioner
Trailer Mounted, Cool Mode Only
______________________________________________________________________________
JANUARY 20, 2004
SECTION 2 - 1
PAGE 21
the system is not to be recharged immediately, the system may be sealed by
back setting the service access valves and plugging or capping all open
gauge ports or connections.
J. Preventing Moisture and Air Entry:
Whenever the refrigeration system is opened, care must be taken to prevent
the entry of moisture and/or air into the system. The filter-drier in the system
is designed to remove particles and small amounts of moisture, which may
enter the system during minor servicing or fault conditions. Major moisture
intrusion through fault or contamination may require complete system
evacuation for moisture removal. Perform
Refrigeration System Evacuation
procedure, paragraph 3.I. in this Section.
Moisture in a refrigerant system can be classified as visible and invisible.
Rarely is liquid water found in a system. Normally all intrusive moisture will be
in the form of vapor. A single drop of moisture in a system can cause "freeze-
ups". Moisture can be picked up by the refrigerant and transported through
the lines as a fine mist, causing ice crystals to form at the point of expansion
(expansion valve). These ice crystals will retard or stop the refrigerant flow,
causing a reduction or complete loss of cooling. As the expansion valve
warms due to the lack of refrigerant, the ice melts and passes through the
expansion valve. The moisture will then cycle through the system until it again
returns to the expansion valve, and the freeze-melt cycle is repeated. The
result is intermittent and inefficient cooling.
Moisture, combined with refrigerants, can create acids, which in turn greatly
increase metal and copper-plating corrosion in the system. Often, the extent
of corrosion damage is not apparent until severe damage has occurred.
Refrigerant oil has an attraction for moisture and will absorb it rapidly if left
open to the atmosphere. Water-formed acids mix with refrigerant oil, forming
a closely bonded mixture of fine globules. The effect is called "sludging" and
greatly reduces the lubricating ability of the oil. The corrosion caused by the
presence of this moisture in the form of "sludge" can plug fine strainers,
expansion valves, and capillary tubes. Because this sludge contains acids, it
will corrode whatever it clings to, accelerating system damage. It is imperative
to service the system using only fresh oil from unopened containers.
The most effective means to remove moisture from a system is using a high
(deep) vacuum pump. A high vacuum pump is capable of removing all
moisture from a hermetic system by reducing internal system pressures to the
boiling point of water at normal temperatures. The vacuum pump does not
"suck out" the liquid moisture, but rather causes it to boil into a vapor state at
which time it can be harmlessly removed from the system and exhausted
through the vacuum pump.
