CHARGING THE SYSTEM
One of the test questions states, "Before charging a refrigeration unit, the refrigerant charging lines should be purged with the refrigerant". New laws regarding refrigerants require all charging lines or hoses to be equipped with valves which seal the lines when they are not connected.
The amount of refrigerant charge must be sufficient to maintain a liquid seal between the condensing and the evaporating sides of the system. When the compressor stops, under normal operating conditions, the receiver of a properly charged system is about 85% full of refrigerant. The proper charge for a specific system or unit can be found in the manufacturer's technical manual or on the ship's blueprints. A refrigeration system must have an adequate charge of refrigerant at all times; otherwise its efficiency and capacity will be impaired.
Low side passive charging of a refrigeration system may be speeded up by warming the service cylinder with hot water to help boil off the liquid. The safest and quickest method of adding refrigerant to a refrigeration system is to add the refrigerant through the charging valve as a liquid.
A refrigeration system should not be charged if there are leaks or if there is reason to believe that there is a leak in the system. The leaks must be found and corrected. A system should be checked for leaks immediately following, or during the process of charging.
Container Refrigeration
If an evaporator or condenser coil of a container refrigeration system becomes dirty and requires cleaning, one of the suggested methods is to use the high pressure wash system.
When a thermostatic expansion valve is installed in a container refrigeration system, the sensing bulb may not require insulation if the bulb is installed outside of the cooled air stream. If the evaporator coil horizontal return line of a container refrigeration system is less than 0.874" (2.21 cm) in diameter, the thermostatic expansion valve sensing bulb should be placed on the upper surface of the line.
SAFETY PRECAUTIONS
Secure and tag the electrical circuit of the system before working any shipboard system, to prevent damage to the equipment, and injury to personal.
On all vessels equipped with refrigeration units of over 20 cubic foot capacity, a gas mask suitable for protection against each refrigerant used, or a self contained breathing apparatus must be provided.
Use chemical safety goggles or a full face shield and rubber gloves while handling refrigerant.
Ammonia vapors in a low concentration can cause death, will dissolve in perspiration and cause caustic burns, and can burn or explode.
Coast Guard Regulations (46 CFR) require a method for the relief of an over-pressurized refrigeration system. A rupture disk may be fitted in series with the relief valve.
Overfilling a refrigerant container is extremely dangerous due to the high pressures generated by hydrostatic pressure of the expanding liquid.
Low pressure refrigeration containers used for transportation are not refillable. They rupture disc set for 15 Psig, and are not to be heated, or stored in temperatures over 125°F. Containers are to be pumped down to 0 Psig or below, and disposed of with the valve opened.
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