You will need some very specific training before you become a good refrigeration system operator. First, you need a lot of practical experience on the systems. Second, you need to pay close attention to the procedures followed by qualified personnel.

Your first responsibility with an R-12 system will probably require you to check temperatures and pressures, maintain the plant operating log, detect symptoms of faulty operation, and check conditions in the spaces or units being cooled. The intervals of time between plant inspections will vary depending on the purpose of the plant. The temperatures and pressures throughout the system and the oil level in the compressor crankcase must be checked every hour. The results should be recorded unless watch-standing instruc-tions specify otherwise. These checks allow operating personnel to determine whether the plant is operating properly. One of the best methods for checking is to compare the existing temperatures and pressures with those recorded when the plant was known to be operating properly, under conditions similar to the present conditions.

AUTOMATIC OPERATION OF AN R-12 REFRIGERATION PLANT

After you have obtained the prescribed operating pressures and temperatures with the compressor running in MANUAL, place the selector switch in the AUTOMATIC position. A refrigeration compressor should NEVER be left unattended when in the MANUAL mode of operation.

You should remember from our discussion that the suction-pressure control (low-pressure cutout switch) is connected electrically to start and stop the compressor automatically on the basis of load conditions. If the automatic control valves and switches are in proper adjustment, the operation of the plant, after proper starting, should be entirely automatic.

When you set the selector switch for automatic operation, the water failure switch, the high-pressure cutout switch, or the low-pressure cutout switch will close and energize their respective control circuits. In some installations, the supply of condenser cooling water comes directly from a centrifugal pump or from the fire and flushing main. If cooling water in your system comes from the fire and flushing main, you must open the pump controller switch manually. The water failure switch must remain closed regardless of the source of condenser cooling water.

In systems that are not equipped with water regulating valves, normal operating conditions will generally produce condensing pressures of less than 125 psi. This happens because the condensing water temperature is usually less than 85F. If your system does have these valves, you should adjust them to maintain the condensing pressure at 125 psi. With the valves adjusted properly, the quantity of cooling water will decrease rapidly with decreasing circulating water temperatures. In systems equipped with air-cooled condensers, condensing pressures may exceed 125 psi when the temperature of the surrounding air is higher than normal.

Only one compressor should serve a cooling coil circuit. When compressors are operated in parallel on a common cooling circuit, lubricating oil may be transferred from one compressor to another. This may cause serious damage to all compressors on the circuit.

An R-12 compressor should not remain idle for an extended period of time. When a plant has two or more compressors, you should operate them alternately. You should make certain that the total operating time on each of the compressors is approximately the same. (An idle compressor should be operated at least once a week.)