4. Close the discharge gage line and open the discharge  line  stop  valve. 5.  Remove  all  oil  from  the  exterior  of  the compressor, and test the compressor joints for leakage, using the halide leak detector. CLEANING SUCTION STRAINERS When putting a new unit into operation, the suction strainers should be cleaned after a few hours of operation. Refrigerants have a solvent action and will loosen any foreign matter in the system. This foreign matter will eventually reach the suction strainers and after a few days of opera- tion, the strainers will need cleaning. Strainers should be inspected frequently during the first few weeks of plant operation, and then cleaned as found  necessary. The suction strainers are located either in the compressor housing or in the suction piping. The procedure for cleaning a strainer is as follows: 1. 2. 3. 4. 5. 6. Pump down the compressor. Slowly bleed pressure from unit. Remove  the  strainer  and  inspect  it  for foreign matter. Clean the strainer screen by dipping it in an approved solvent and then allow it to dry. Replace the strainer and evacuate the air from the compressor. Test the housing for leaks by wiping up all oil and then using a halide leak detector. CONDENSERS The compressor discharge line terminates at the  refrigerant  condenser.  In  shipboard  R-12 installations,  these  condensers  are  usually  of  the multipass  shell-and-tube  type,  with  water  cir- culating  through  the  tubes.  The  tubes  are  ex- panded into grooved holes in the tube sheet so as  to  make  an  absolutely  tight  joint  between  the shell and the circulating water. Refrigerant vapor is admitted to the shell, and condenses on the outer surfaces of the tubes. Any  air  or  noncondensable  gases  which  may accidentally  enter  the  refrigeration  system  is drawn  through  the  piping  and  eventually  dis- charged into the condenser with the R-12 gas. The air  or  noncondensable  gases  accumulated  in  the condenser are lighter than the refrigerant gas and rise to the top of the condenser when the plant is  shut  down.  A  purge  valve,  for  purging  the refrigeration system (when necessary), is installed either at the top of the condenser, or at a high point in the compressor discharge line. CLEANING CONDENSER TUBES In  order  to  clean  the  condenser  tubes properly, it is necessary first to drain the cooling water from the condenser and then disconnect the water  connections  and  remove  the  condenser heads. When you remove the condenser heads, be careful not to damage the gaskets between the tube sheet and the water side of the condenser heads. Tubes should be inspected as often as prac- ticable and be cleaned when necessary, by using any approved method. Use rubber plugs and an air or water lance when it is necessary to remove foreign deposits. Although it is essential that the tube surfaces be kept clear of particles of foreign matter, care must be taken not to destroy the thin protective coating on the inner surfaces of the tubes. When the tubes become badly corroded, they  should  be  replaced  in  order  to  avoid  the possibility  of  losing  the  R-12  charge  and  admit- ting salt water into the R-12 system. CLEANING   AIR-COOLED CONDENSERS Although the large plants are equipped with water-cooled  condensers,  the  auxiliary  units  are commonly  provided  with  air-cooled  condensers. The  use  of  air-cooled  condensers  eliminates  the necessity  for  circulating  water  pumps  and  piping. The exterior surface of the tubes and fins on a condenser should be kept free of dirt and any matter that might obstruct heat flow and air cir- culation. Brush the finned surface clean with a stiff bristle brush as often as necessary. Use low pressure air to remove dirt in hard to reach places on the condenser. When installations are exposed to  salt  spray  and  rain  through  open  doors  or hatches, take care to minimize corrosion of the exterior  surfaces. ENGINEMAN  1  &  C 6-8