Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTS 



VAPOR 



REFRIGERANT 



NLET 



OUTLET 



INLET 



Figure 19-7.— Water-cooled condenser for R-12 refrigeration system. A. Cutawayview. 

 B. Water-flow diagram. C. Arrangement of head joints. D. Position of zincs. 



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the low pressure cutout switch closes, starting 

 the compressor again and repeating the cycle. 

 A high pressure cutout switch is connected 

 to the compressor discharge line to protect the 

 high side of the system against excessive pres- 

 sures. This switch is very similar to the low 

 pressure cutout switch; however, the low pres- 

 sure cutout switch is designed to close when 

 the suction pressure reaches its upper normal 

 limit, whereas the high pressure cutout switch 

 is designed to open when the discharge pres- 

 sure is too high. The high pressure cutout 

 switch is normally set to stop the compressor 



when the pressure reaches 160 psi and to start 

 it again when the pressure drops to 140 psi. As 

 previously noted, the low pressure cutout switch 

 is the com.pressor control for normal operation 

 of the plant; the high pressure cutout switch, on 

 the other hand, is a safety device only and does 

 not have control of compressor operation under 

 normal conditions. 



A spring-loaded relief valve is installed in 

 the compressor discharge line as an additional 

 precaution against excessive pressures. The 

 relief valve is set to open at about 225 psi; 

 therefore, it functions only in case of failure or 



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