Chapter 6—REFRIGERATION AND AIR CONDITIONINGfalling temperatures until the water in the systemstarts to boil.When most of the evaporated moisture hasbeen evacuated from the system, the indicator willshow a decrease in temperature. As soon as thetemperature reaches 35 °F (0.2 inch Hg, absolute),admit dry air through a chemical dehydratorinto the system at a point farthest from the pump.As the pump continues operating, the dry air willmix with and dilute any remaining moisture.Secure the opening which feeds the dry air to thesystem. The system must continue evacuating untilthe indicator again shows a temperature of 35 °F.At this time, the dehydration process is complete.Close the valves and disconnect the vacuumpump.as activated alumina and silica gel. However,when special drying agents are employed theyshould be reactivated in accordance with thespecific instructions furnished by themanufacturer.After reactivation, the drying agent should beplaced back in the dehydrator shell and sealed asquickly as possible, in order to prevent absorp-tion of atmospheric moisture. When the dryingagent becomes fouled or saturated with lubricatingoil, it must be replaced with a fresh charge, orwith a dehydrator cartridge, taken from a sealedcontainer.Sometimes it is impossible to obtain atemperature as low as 35 °F in the vacuumindicator. The probable reasons for this and thecorrective procedures to take, are as follows:1. Excess moisture is present in the system.Because of the acid being formed, the dehydra-tion procedure should be conducted for longerperiods.Remember that the dehydrators that arepermanently installed in refrigeration systems ofnaval ships are designed to remove only theminute quantities of moisture unavoidablyintroduced in the system. Extreme care must betaken to prevent moisture, or moisture-laden air,from entering the system.CLEANING THE SYSTEM2. Absorbed refrigerant is present in thelubricating oil contained in the compressorcrankcase. Remove the lubricating oil from thecrankcase before proceeding with the dehydrationprocess.3. Air is leaking into the system. The leakmust be found and stopped. It will be necessaryto repeat the procedure required for detectingleaks in the system.4. Inefficient vacuum pump or defectivevacuum indicator. The defective unit(s) should berepaired or replaced.Systems may accumulate dirt and scale as aresult of improper procedures used during repairor installation of the system. If such dirt isexcessive and a tank-type cleaner is available, con-nect the cleaner to the compressor suction strainer.Where such a cleaner is not available, insert a hardwool felt filter, about 5/16 inch thick, in the suc-tion strainer screen. The plant should then beoperated with an operator in attendance, for atleast 36 hours or until cleaned, depending uponthe size and the condition of the plant.Immediately after each period of use, or afterthe system has been opened for repairs, the dry-ing agent in the dehydrator should be replaced.If a replacement cartridge is not available, the dry-ing agent can be reactivated and used until areplacement is available.AIR CONDITIONING CONTROLReactivation is accomplished by removing thedrying agent and heating it, for 12 hours, at atemperature of 300°F to bake out the moisture.The drying agent may be placed in an oven, ora stream of hot air may be circulated through thecartridge. These methods are satisfactory for reac-tivating commonly used dehydrating agents suchMost of the information presented to thispoint applies to the refrigeration side of a system,whether it is used for a refrigeration plant or forair conditioning. The compressor controls forboth type systems are nearly identical, however,the devices used to control space temperatures dif-fer. A two-position control, sometimes called theon/off control, is used for the automatic controlof most shipboard air conditioning systems.6-15
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