valve without having to replace the entire assembly.
When replacement of an expansion valve is necessary,
you must replace the unit with a valve of the same
capacity and type.
ADDITIONAL SYSTEM MAINTENANCE
In addition to the maintenance of the components
previously described, other parts of the system will need
periodic maintenance to keep the plant operating
Vibration may cause leakage in the piping system.
This leakage may allow air and moisture to be drawn in
or a loss of refrigerant charge. If this happens, the plant
operation will become erratic and inefficient, and the
cause of trouble must be corrected.
CHARGING THE SYSTEM
Information concerning the charging of
refrigeration systems may be found in NSTM, Chapter
516, Refrigeration System. The amount of refrigerant
charge must be sufficient to maintain a liquid seal
between the condensing and evaporating sides of the
system. Under normal operating conditions, when the
compressor stops, the receiver of a properly charged
system is about 85 percent full of refrigerant. The proper
charge for a specific system or unit can be found in the
manufacturers technical manual or on the ships
A refrigeration system should not be charged if it
has leaks or if you have a reason to believe the system
has a leak. The leaks must be found and corrected.
Immediately following-or during-the process of
charging, you should carefully check the system for
A refrigeration system must have an adequate
charge of refrigerant at all times; otherwise, its
efficiency and capacity will be impaired.
PURGING THE SYSTEM
To determine if the system contains noncondensable
gases, operate the system for 30 minutes. Stop the
compressor for 10 to 15 minutes, leaving all the valves
in their normal positions. Observe the pressure and
temperature as indicated on the high-pressure gauge.
Read the thermometer in the liquid line, or read the
temperature of the cooling water discharge from the
condenser. Compare the temperature reading with the
temperature conversion figures shown on the discharge
pressure gauge. If the temperature of the liquid leaving
the receiver is more than 5°F lower than the temperature
corresponding to the discharge pressure, the system
should be purged. Pump the system down and secure the
compressor; then open the purge valve on the condenser.
Purge very slowly, at intervals, until the air is expelled
from the system and the temperature difference drops
CLEANING LIQUID LINE STRAINERS
Where a liquid line strainer is installed, it should be
cleaned at the same intervals as the suction strainer. If a
liquid line strainer becomes clogged to the extent that it
needs cleaning, a loss of refrigeration will take place.
The tubing on the outlet side of the strainer will be much
colder than the tubing on the inlet side.
To clean the liquid line strainer, secure the receiver
outlet valve and wait a few minutes to allow any liquid
in the strainer to flow to the cooling coils. Then close
the strainer outlet valve and very carefully loosen the
cap that is bolted to the strainer body. (Use goggles to
protect your eyes!) When all the pressure is bled out of
the strainer, remove the cap and lift out the strainer
screen. Clean the strainer screen with an approved
solvent and a small brush. Reinstall the spring and
screen in the strainer body; then replace the strainer cap
loosely. Purge the air out of the strainer by blowing
refrigerant through it; then tighten the cap. After the
assembly is complete, test the unit for leaks.
CLEANING OIL FILTERS AND STRAINERS
Compressors arranged for forced-feed lubrication
have lubricating oil strainers in the suction line of the
lube-oil pump. An oil filter may be installed in the pump
discharge line. A gradual decrease in lubricating oil
pressure indicates that these units need cleaning. This
cleaning is done in much the same manner as described
for cleaning suction strainers.
When cleaning is necessary, drain the lubricating oil
in the crankcase from the compressor. Add a new charge
of oil, equal to the amount drained, before restarting the
unit. When the compressor is put back into operation,
adjust the lube-oil pressure to the proper setting by
adjusting the oil pressure regulator.
MAINTAINING COOLING COILS
You should inspect the cooling coils regularly and
clean them as required. Defrost the cooling coils as often
as necessary to maintain the effectiveness of the cooling
surface. Excessive buildup of frost on the cooling coils