FARM STORAGES FOR APPLES 31 



will turn blue if exposed to ammonia fumes, and by holding such paper near sus- 

 pected points, the leak can be located with ease. The tests used with common 

 refrigerants are listed below: 



Ammonia Litmus paper or sulfur candle 



Sulfur Dioxide Ammonia water 



Methyl Chloride Alcohol flame 



Freon Alcohol flame 



If a sulfur candle is brought near an ammonia leak, a white smoke is formed. 

 Likewise, if ammonia water is brought near a sulfur-dioxide leak, a white smoke 

 is produced. Methyl chloride and freon give a blue-green tinge to an alcohol 

 flame. Special alcohol blow torches are available for testing purposes. 



Leaks develop usually in the stuffing boxes of the compressor shaft and in the 

 hand valves. If moderate tightening of the glands decs not stop the leaks, it 

 is necessary to renew the packing. 



Lubrication 



Compressors must be supplied with a special oil, and none other should be used. 

 Ammonia compressors have oil gauges indicating the proper height to be carried 

 in the crank case, but in systems using other refrigerants the oil circulates with the 

 refrigerant, and usually oil is put in only as new refrigerant is added. Specific 

 directions should be obtained from the manufacturer for the lubrication of fans 

 and motors. 



Defrosting 



In order that a refrigerating system may work efficiently, it is necessary that 

 the cooling coils be reasonably free from frost, particular!}- in blowers. A heavy 

 accumulation of frost insulates the coils and retards the passage of heat from the 

 air to the refrigerant. The air then leaves the blower at a higher temperature 

 than would be the case if the coils were free from frost. A heavy accumulation 

 of frost also clogs the air passages in the blower, with the result that less than the 

 normal amount of air is forced over the coils. This in turn reduces the amount 

 of heat taken up by the coils. 



There are three common means for defrosting: 



L Defrosting by means of a time clock, the refrigerant being shut off from the 

 blower for a brief time at regular intervals without stepping the fan. 



2. Shutting down the compressor and operating the blower fan in the normal 

 manner and depending upon the air within the room to melt the frost. This is 

 the same as No. 1 except that the operation is not automatic. Plans 1 and 2 

 are used with small plants. 



3. Shutting down the compressor and operating the fan so as to draw air 

 from outdoors over the coils. This plan warms up the storage unnecessarily 

 and may also lower humidit> . 



4. Defrosting by the introduction of hot refrigerant into the cooling coils. 

 The plan requires special piping and is the one most generally used on the larger 

 plants where defrosting must be done in the minimum time. This method should 

 not be used except in plants having two or more diffuser units. 



