ASSIGNMENT  4 Textbook  Assignment: "Refrigeration  and  Air  Conditioning,"  "Compressed  Air  Systems," "Laundry,  Mess  Decks,  Galley,  and  Scullery  Equipment,"  "Other Auxiliary  Equipment,"   and  "Lathe  and  Machining  Operations,"  chapters 5 through 9, pages 5-9 through 9-20. 4-1. Which  of  the  following  conditions may  be  caused  by  excessive  buildup of frost on the cooling coils? 1. Low suction pressure 2. High suction pressure 3. Low suction temperature 4. High condensing pressure 4-2. The  maximum  time  between  defrosting of the cooling coils depends on which  of  the  following  factors? 1. Amount of refrigerant in the system 2. Moisture content of the supplies placed in the box 3.    Amount of heat to be removed 4. All of the above 4-3. You  must  defrost  the  cooling  coils before the frost reaches what maximum  thickness? 1. 1/8 inch 2. 3/16 inch 3. 1/4 inch 4. 5/16 inch IN  ANSWERING  QUESTION  4-4,  REFER  TO  FIGURE 5-4 OF THE TEXTBOOK. 4-4. Approximately  how  many  inches  of mercury  represent  the  difference  in temperature between points B and D? 1. 0.200  inch  absolute 2. 0.232  inch  absolute 3. 0.436  inch  absolute 4. 0.640  inch  absolute 4-5. While  you  are  evacuating  and dehydrating  a  refrigeration  system, the  vacuum  indicator  fails  to attain 35°F. Which of the following  conditions  may  be  the cause of this failure? 1. Lack of lubricating oil in the compressor  crankcase 2. Lack of moisture in the system 3. Presence of R-12 in the lubricating  oil 4. Each of the above 4-6. To  be  properly  reactivated, dehydrating  agents  should  be  heated (a) at what specific temperature and (b) for what approximate length of time? 1. (a) 200°F; (b) 12 hr 2. (a) 300°F; (b) 12 hr 3. (a) 400°F; (b) 6 hr 4. (a) 500°F; (b) 6 hr 4-7. If you do not have a tank-type cleaner, you can clean an R-12 system by which of the following methods? 1. By  flushing  boiling  water through  the  system  three  times 2. By blowing hot air through the system for 24 hours 3.    By inserting a hard, wool felt filter in the suction strainer screen and operating the plant 4. Each of the above methods 4-8. On  the  two-position,  dual  control (2PD), which of the following system types uses one common cooling  coil  to  service  several different  spaces? 1. 1 2. 2 3. 3 26