In addition to the maintenance of the components previously described, other parts of the system will need periodic maintenance to keep the plant operating properly.

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 blueprints.

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 leaks.

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 5F 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 below 5F.