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Pressure   Regulator   Valve
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TM-5-4120-239-14 Refigeration Unit Mechanical Panel Mounted For Refrigerator Prefabricated Eletric Motor Driven KECO Model F10000R-6 NSN 4110-01-077-B203 Gasoline Engine Driven Manual
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Figure  6-1.  Disrharging  and  purging  refrigerant  system,
CHAPTER  6 REPAIR  INSTRUCTIONS Section  1.   REFRIGERATION   SYSTEM 6-1. General The   refrigerant   system,   illustrated   by   the refrigerant  flow  diagram  (fig.  5-1  ),  is  a  mechanical, vapor cycle-type circuit consisting   of the evaporator, thermal  expansion valve, motor compressor,   condenser,   and   the   necessary   valves a  nd  cutout  devices  for  automatic  control  during operation.  The  thermal  expansion  valve  releases high-pressure   liquid   refrigerant   into   the   evaporator at   reduced   -pressure.   The   liquid   refrigerant   begins to  vaporize  by  absorbing  heat  from  the  air  passing over   the   external   surface   of   the   evaporator   core. The   heater   vapor   is   sucked   out   of   the   evaporator suction  by  the  motor  compressor  and  forced  into the  condenser  section  under  high  pressure  where  it is   cooled   and   condensed   back   into   a   liquid.   The heat   released   during   condensation   is   carried   off   by the   condensing   air   stream.   The   liquid   refrigerant flows  from  the  condenser  to  a  receiver,  to  a  sub- cooler,  and  then  to  the  thermal  expansion  valve.  If the   temperature   control   switch   (evaporator   return air   thermostat)   become   satisfied,   or   the   evaporator return   air   temperature   is   lower   than   the   control switch   set   point,   the   refrigerant   system   will   switch to   a   by-pass   condition.   The  temperature  control switch   will   activate   the   normally   open   liquid   by- pass  solenoid  valve,  closing  the  valve,  and  therefore shutting  off  the  evaporator  section  of  the  unit.  The motor  compressor  will  continue  to  pump  as  usual and  the  suction  pressure  will  begin  to  drop.  When  it reaches   approximately   65   psig,   the   pressure regulating   valve   will   start   to   open   in   an   effort   to maintain   the   suction   pressure   above   55   psig (approx.  ).  As  the  suction  temperature  increases,  due to   the   pressure   regulating   valve   opening,   the quench  expansion  valve  will  start  to  meter  liquid refrigerant  into  the  suction  line  in  an  effort  to maintain   the   suction   temperature   below   75°   F (approx.  )  or  30°F  super-heat  (approx.  ).  This  action (the  pressure  regulator  and  quench  valve  actions)  is totally  automatic  and  also  may  occur  at  extreme conditions   in   an   attempt   to   maintain   the   suction pressures   (even   during   the   cooling   mode)   at   a condition  above  55  psig  and  the  suction  tem- peratures   (measured   at   the   quench   bulb   well) below  75°  F.  The  condenser  louvers  are  operated  by a   refrigerant   powered   piston located   in   high pressure   part   of   the   system.   This   piston   should   be fully   extended   (louvers   open   80°F   approx.)   at   250 psig   head   pressure   and   fully   closed   at   165   psig. Failure   to   perform   this   function   could   result   in icing  of  the  evaporator  coil  and  /  or  cutout  on  the low   pressure   cutout. 6-2.   Pressure   Testing   the   Refrigerant   System a.  GeneruL  A  pressure  test  will  indicate  whether the  air  conditioner  is  operating  at  normal  or  ab- normal   pressures.   When   the   air   conditioner   is   not operating   at   normal   pressures   the   cause   should   be ascertained  and  corrected.  Refer  to  Table  5-1  for troubleshooting   chart. b.  System  Pressure  Test.  Remove  caps  from  high and  low  pressure  charging  valves  (fig.  5-71,  connect suction  and  discharge  pressure  gages  to  their respective   charging   valves.   Compare   the   gage reading   with   the   normal   range   of   system   pressure shown   in   Table   6-1. 6-3.   Servicing   Refrigerant   System a.   General,   When   the   air   conditioner   must undergo   maintenance   that   requires   opening   the system,  the  system  must  be  discharged  prior  to maintenance   and   purged   and charged after maintenance. This   paragraph   covers   the   basic procedures   involved   in    servicing   the   refrigerant system. b.   Discharging   and   Purging   System.   Refer   to figure  6-1  for  discharging  or  purging  the  refrigerant system. 6-1

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