8-36. If you do not have a tank-type cleaner, you can clean an R-12 system by which of the  following  means? 1. By  flushing  boiling  water  through  the system  three  times 2. By  blowing  hot  air  through  the  system with  a  blower  for  24  hours 3. By  inserting  a  hard  wool  felt  filter in  the  suction  strainer  screen  and operating  the  plant  with  an  operator 4. By  using  any  one  of  the  above  methods Question 8-37 is to be judged True or False. 8-37. The  2  PD  air  conditioning  control  may  be used  where  one  common  cooling  coil  serves several  different  spaces. 8-38. How  should  you  clean  the  sensing  elements in  humidistats? 1. Use a soft brush 2. Blow  gently  with  air 3. Spray  with  soap  and  water  solution 4. Use a hard brush Learning  Objective:  Recognize  troubles that  may  be  encountered  with refrigeration  and  air  conditioning systems, and  point  out  corrective measures  that  may  be  required. 8-39. What  should  you  do  to  correct  low condensing  pressure  in  an  operating refrigeration   system? 1. Reduce  the  water  supply 2. Increase  the  water  pressure 3. Clean  the  valves  and  the  valve  nests 4. Adjust  the  high-pressure  cutout switch 8-40. Insufficient  refrigerant  in  a refrigeration  plant  may  cause  which  of the  following  problems? 1. High  discharge  pressure 2. Low  suction  pressure 3. Frosting  of  the  crankcase 4. High  temperature  of  the  overboard water 8-41. Which  of  the  following  actions  should  you take  to  correct  a  low  condensing  pressure in  a  refrigeration  system? 1. Add  refrigerant 2. Purge  the  condenser 3. Increase  the  compressor  speed 4. Adjust  the  thermostatic  expansion valve 8-42. 8-43. 8-44. 8-45. In  an  R-12  refrigeration  plant,  what  is the  probable  cause  if  the  compressor  runs continuously? 1. An  open  solenoid  valve  switch 2. An  inadequate  supply  of  refrigerant 3. Clogged  condenser  tubes 4. An  excess  of  liquid  refrigerant What  are  the  two  symptoms  that  indicate an  inadequate  supply  of  water  is  passing through  the  condenser  of  a  refrigeration plant? 1. Excessively  low  temperature  of  the overboard  water  and  low  discharge pressure 2. High  suction  pressure  and  high temperature  of  the  suction  line 3. High  condensing  pressure  and compressor  short  cycling  on  high pressure   switch 4. High  suction  line  temperature  and high  discharge  pressure The cut-in point is set too high on the low  pressure  control  switch  to  an  R-12 refrigeration   system. How will this affect  the  functioning  of  the  compressor? 1. The  compressor  will  short  cycle 2. The  compressor  will  not  operate 3. The  compressor  will  operate  unloaded 4. The  compressor  will  operate continuously Which  of  the  following  conditions  is probably  caused  by  an  improperly  adjusted pressure regulating valve in a refrigeration   system? 1. The  refrigerant  is  bubbling 2. The sudden loss of oil from the crankcase 3. The  compressor  continues  to  operate unloaded 4. The oil fails to return to the compressor   crankcase Learning Objective: Point out the general  practices,  maintenance requirements,  and  tasks  necessary  for proper  operation  of  air  compressors  and related  system  components,  and  identify the  safety  precautions  to  be  followed. 52