4-9. What  technique  must  you  use  to clean  the  sensing  elements  in  the humidistats? 1. Use of a soft brush 2. Use of gently blown air 3. Use of a spray of soap and water  solution 4. Use of a hard brush 4-10. To  correct  a  low  condensing pressure  in  an  operating refrigeration  system,  you  should perform which of the following actions? 1. Reduce the water supply 2. Increase  the  water  pressure 3. Clean the valves and the valve seats 4. Adjust the high-pressure cutout switch 4-11. 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 4-12. 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 4-13. In  an  R-12  refrigeration  plant,  a compressor  runs  continuously. What is the probable cause? 1. An open solenoid valve switch 2. An inadequate supply of refrigerant 3. Clogged condenser tubes 4. An excess of liquid refrigerant 4-14. Which  of  the  following  symptoms indicates  that  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  the high-pressure   switch 4. High  suction  line  temperature and  high  discharge  pressure 4-15. The cut-in point is set too high on the  low-pressure  control  switch  of an R-12 refrigeration system. How will  this  effect  the  functioning  of the  compressor? 1. It will short cycle 2. It will not operate 3. It  will  operate  unloaded 4. It  will  operate  continuously 4-16. Which  of  the  following  conditions is  probably  caused  by  liquid refrigerant  slugging  back  to  the compressor crankcase of a refrigeration  system? 1. Bubbles  in  the  refrigerant 2. A sudden loss of oil from the crankcase 3. The compressor continues to operate  unloaded 4. Failure of oil to return to the compressor   crankcase 4-17. Aboard Navy ships, in which of the following  situations  would  you  most likely use MP air? 1. To clean machinery 2. To  start  diesel  engines 3. To  operate  pneumatic  tools 4. Each of the above 27