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TM 5-4120-270-15 mation of condensation on the inside walls of the tubing. Plug   or   cap   all   openings   as   a   part   is   removed   to minimize the entry of dirt and moisture. d.    Use  a  silver  solder  on  all  soldered  connections. Easy-Flo  silver  solder  (or  equivalent)  with  a  50  percent silver   capacity   and   a   melting   point   of   approximately 1160°F is recommended.  Continually pass dry nitrogen through   the   tubing   or   connections   being   soldered   to prevent formation of harmful copper oxides. e.  After assembly of any flanged joint, apply one coat of Amer-coat No.  40 to the joint. f.      After   assembly   of   piping,   coat   all   copper   to- aluminum  joints  with  3  coats  Amer-coat  No.  40  for  a distance of one inch on each side of joint as well as the joint. Note.        Amer-coat    may    be    force    dried    at    a maximum  temperature of 140°F. g.  When removing and installing the solenoid valves, direct flame away from the valve body to protect it from heat  damage.    Keep  the  flame  on  the  outside  of  the distributor   when   disassembling   or   reassembling   the expansion valve. h.  No metal to metal contact is allowable on capillary tubes; use tape to prevent such contact. 6-17.  Thermal Expansion Valves a.    General.    A  4  1/2-ton  thermal  expansion  valve controls  the  rate  of  flow  of  liquid  refrigerant  into  the evaporator  coil  during  the  cooling  cycle  of  operation. The 2.1 ton thermal expansion valve functions when the unit is in the bypass cycle of operation.  Each expansion valve is provided with a superheat setting or adjustment (10°F   for   each   model)   to   assure   efficiency   in   the refrigerant system. Note.        A    gas    is    superheated    whenever    its temperature is higher than the temperature corresponding  to  its  pressure  at  saturation.    Example: Refrigerant-22 at 69 pounds pressure has a temperature of 40°F.  If the suction pressure gage reads 69 pounds and the temperature of the suction tube reads 50°F, the gas is superheated 10OF. b.    Adjustment.    Refer  to  figures  6-10    and  6-11 and  check  and  adjust  the  superheat  setting  of  the  4 1/2ton  thermal  expansion  valve.    The  2.1  ton  thermal expansion valve adjusts in the same manner. c.  Testing. (1)   Stop   the   air   conditioner   and   allow   the suction line to warm up to ambient temperature. Remove the  sensing  bulb  from  its location against the suction line and place in an ice-water bath (820F). (2)    Start    the    air    conditioner,    remove    the sensing bulb from the ice-water bath and warm by hand while   feeling   the   suction   line.      If   the   suction   line temperature drops, the valve is operating correctly.  Stop air conditioner and reinstall the sensing bulb. (3) If there is little or no change in suction line temperature,    the    valve    is    defective    and    must    be replaced. Caution:  Do  not  warm  sensing  bulb  in  hand longer   than   necessary   to   check   operation   of   the valve.    The  valve  is  wide  open  or  nearly  so  during this   procedure   and   excessive   flood-back   of   liquid refrigerant   into   the   suction   line   will   damage   the compressor. Figure 6-10.  Thermal Expansion valve superheat adjustment 6-12

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