TM  5-4120-259-15 (6) (7) (8) Caution: Failure to maintain a neu- tral  atmosphere  within  tubing  during brazing can cause copper oxidation, producing  harmful  chemical  reac- tions  in  the  compressor  lubricating oil, and a deterioration of the refrig- erant resulting in harmful acids and general contamination of the system. Apply   heat   with   an   acetylene   gas torch,   using   a   neutral   to   reducing flame  (a  greenish)  feather  extending from  the  tip  of  the  inner  cone  indi- cates   a   slightly   reducing   flame.) Heat   the   fitting   and   tubing   evenly over   the   full   circumference   of   the joint,  keeping  the  torch  flame  in  mo- tion   to   assure   even   distribution   of heat. Test the temperature by touch- ing the edge of the joint with brazing alloy.  Do  not  apply  the  flame  to  the alloy.  When  the  alloy  starts  to  melt and run, the heat is right for brazing. Caution: Use a piece of asbestos sheeting to protect other portions of the system from flame damage during brazing. Feed  brazing  alloy  cautiously.  Alloy will   flow   freely   at   right   tempera- ture   but   will   burn   when   too   hot. When   joint   is   full,   brazing   material will    appwm    in    a complete ring around  the  edge  of  the  fitting. Be sure that some part of the system Wipe  excess  material  from  joint  with rag  or  brush  while  joint  is  still  hot. Inspect   joint   to   make   sure   it   has properly   filled. 97.  Charging  the  System The system must be charged witih the cor- rect   amount   of   Refrigerant-22.   The   correct amount  is  16  lbs.  Make  charging  connection as shown by figure 37. Charge by the follow- ing  procedure. a. Connect a bottle of Refrigerant-22 to the charging  panel  (figure  37)  and  open  valves A   and   B.   Valves   C   and   D   should   remain closed. b. Open  the  valve  on  the  refrigerant  bottle to allow gas to enter the system until the pres- sure  is  equalized  with  that  in  the  cylinder. Caution: The compressor must not be oper- ated before step c has been completed. c. Close valve A. d.  Operate   the   compressor   and   slowly charge into the system, After sufficient refrig- erant has been added, the refrigerant will start building  up  in  the  receiver.  At  this  paint  the discharge presure will continue a steady rise. When  this  condition  exists,  the  unit  is  fully charged. Note.  If   the   unit   is   overcharged,   the   refrigerant is   left   open   to   atmosphere   during brazing. Otherwise   pressure   may build in the system and blow brazing material   from   the   joint. will  fill  up  the  receiver  space  and  back  up  into  the condenser  space.  If  this  happens,  a  sudden  and  ex- cessive  increase  in  discharge  pressure  will  be  noted. If  this  happens,  bleed  the  entire  charge,  and  recharge (paragraphs 95 and 97). Section II. COMPRESSOR 98. General b.  Installation. The   hermetic   compressor   is   hermetically (1) sealed, and if found to be dafective, it must be removed from the refrigerant circuit and a new compressor  installed.  The  new  compressor  will (2) have  been  charged  with  oil  and  nitrogen  gas as a holding charge. 99.  Compressor a. Replacement.  Remove  the  compressor  as (3) shown by figure 28. 56 Using  a  wire  brush  or  crocus  cloth, clean   the   system   suction   and   dis- charge   connections. Crack  the  flare  nut  on  the  charging valve  of  the  new  compressor  to  re- lease   the   nitrogen-holding   charge pressure, then   retighten   the   flare nut. Remove any charging fittings or caps from the compressor and prepare the