Keep the exterior surface of the tubes and the fins on an air-cooled condenser free of dirt or any matter that might obstruct heat flow and air circulation. The finned surface should be brushed clean with a stiff bristle brush as often as necessary. Low-pressure air is very useful in removing  dirt  in  hard-to-reach  places  on  condensers. When  installations  are  exposed  to  salt  spray  and  rain through open doors or hatches, you should take steps to minimize corrosion of the exterior surfaces. Testing For Leaks To prevent serious loss of refrigerant through leaky condenser  tubes,  test  the  condenser  for  leakage  by following the PMS. To   test   for   leaky   condenser   tubes,   drain   the waterside  of  the  condenser.  Then  insert  the  exploring tube of the leak detector through one of the drain plug openings. If this test indicates that Freon gas is present, you can find the exact location of the leak by following these  steps: 1. Remove the condenser heads. 2.   Clean and dry the tube sheets and the ends of the tubes. 3.  Check  both  ends  of  each  tube  with  a  leak detector.  Mark  any  tubes  that  show  leakage.  If  you cannot  determine  that  a  tube  is  leaking  internally  or around the tube sheet joint, plug the suspected tube and again  check  around  the  tube  sheet  joint.  Mark  the adjacent tube, if necessary, to isolate the suspected area. 4.  To  locate  or  isolate  very  small  leaks  in  the condenser tubes, hold the exploring tube at one end of the condenser tube for about 10 seconds to draw fresh air through the tube. Repeat this procedure with all the tubes  in  the  condenser.  Allow  the  condenser  tubes  to remain plugged for 4 to 6 hours; then, remove the plugs one at a time and check each tube for leakage. If a leaky tube  is  detected,  replace  the  plug  immediately  to  reduce the  amount  of  refrigerant  escaping.  Make  appropriate repairs or mark and plug all leaky tubes for later repairs. Plugging or Retubing Condensers The  general  procedures  for  plugging  or  retubing condensers  can  be  found  in  Naval  Ship's  Technical Manual   (NSTM),  Chapter  254,  “Condensers,  Heat Exchangers,  and  Air  Ejectors.” When  plugging  or retubing a specific condenser, follow the procedures in the manufacturer’s technical manual. THERMOSTATIC  EXPANSION  VALVES The  thermostatic  expansion  valve  is  essentially  a reducing valve between the high-pressure side and the low-pressure side of the system. The valve is designed to proportion the rate at which the refrigerant enters the cooling  coil  to  the  rate  of  evaporation  of  the  liquid refrigerant in the coil; the amount depends, of course, on   the   amount   of   heat   being   removed   from   the refrigerated space. When  the  thermostatic  expansion  valve  is  operating properly, the temperature at the outlet side of the valve is  much  lower  than  that  at  the  inlet  side.  If  this temperature difference does not exist when the system is  in  operation,  the  valve  seat  is  probably  dirty  and clogged with foreign matter. Once  a  valve  is  properly  adjusted,  further adjustment should not be necessary. The major trouble can usually be traced to moisture or dirt collecting at the valve seat and orifice. Testing and Adjustment The  thermostatic  expansion  valves  used  in  most shipboard systems can be adjusted by means of a gear and screw arrangement to maintain a superheat ranging from about 4°F to 12°F at the cooling coil outlet. The proper superheat adjustment varies with the design and service operating conditions of the valve and the design of  the  particular  plant.  Increased  spring  pressure increases  the  degree  of  superheat  at  the  coil  outlet. Decreased   spring   pressure   decreases   the   degree   of superheat  at  the  coil  outlet. Some  thermostatic  expansion  valves  have  a  fixed (nonadjustable)   superheat.   These   valves   are   used primarily in self-contained equipment where the piping configuration and evaporating conditions are constant. If  expansion  valves  are  adjusted  to  give  a  high superheat at the coil outlet or if the valve is stuck shut, the amount of refrigerant admitted to the cooling coil will   be   reduced.   With   an   insufficient   amount   of refrigerant, the coil will be “starved” and will operate at a reduced capacity. Also, the velocity of the refrigerant through the coil may not be adequate to carry oil through the  coil.  This  robs  the  compressor  crankcase  and provides a condition where slugs of lubricating oil may be  drawn  back  into  the  compressor.  If  the  expansion valve is adjusted for too low a degree of superheat or if the  valve  is  stuck  open,  liquid  refrigerant  may  flood from the cooling coils back into the compressor. When liquid refrigerant collects at a low point in the suction 5-7