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TM 5-4120-270-15 d. Installation.        Replace    a    defective    coil assembly   and   install   in   reverse   order   of   removal   as illustrated  in  figure  5-13.    Test,  evacuate  and  recharge refrigerating system (para  28, 29, 30). 6-25. Systems Access Valves a. General.      Two   angle-type   access   valves (suction  line  and  discharge  line)  provide  access  to  the refrigerant system. b. Removal. Discharge the refrigerant system  and  refer  to  figure  5-11  and  remove  the  access valves. c. Installation.  Replace a defective valve and install valves in reverse order of removal as illustrated in figure   5-11.      Test,   evacuate   and   recharge   the   unit refrigeration system (para 628, 29, 80). 6-26.  Compressor and Motor Assembly a. General.          The     sole purpose of the compressor  is  to  raise  the  pressure  of  refrigerant  gas from  evaporator  pressure  to  condensing  pressure.    The function of the compressor i ’to deliver refrigerant to the condenser  at  a  pressure  and  temperature  at  which  the condensing  process  can  readily  be  accomplished.    The motor/compressor is a hermetically sealed unit and is not repairable   in   the   field.      An   inoperative   compressor   is usually     due     to     a     mechanical     failure     causing     the compressor   to   freeze,   a   control   failure,   or   a   motor burnout.  If the motor/compressor is mechanically frozen or there has been a motor burnout, the compressor must be   removed    and    replaced.        When    the    motor    of    a hermetic    compressor    fails,    high    temperatures    may develop  within  the  compressor  causing  a  breakdown  of the   oil   and   refrigerant,   resulting   in   formation   of   acid, moisture, and sludge.  All these are extremely.  corrosive and    must    be    flushed    from    the    system.        Repeated burnouts   will   occur   if   all   of   the   contaminants   are   not removed. b. Cleaning and Inspection.  The immediate area    around    the    compressor    mounting     should     be thoroughly  cleaned  and  dried.    Examine  all  connections for foreign matter of any kind.  Inspect area thoroughly. Warning: Avoid bodily contact with the refrigerant,  especially  eye  contact.    Avoid  inhalation  of refrigerant fumes. c. Removal. Discharge the refrigerant system, refer to figure 5-6, and remove the compressor. If there has been a burnout, flush system as described in e below prior to installation of new compressor. d. Installation. Install a replacement compressor in reverse order of removal, as illustrated in figure    5-6.        Pressure    test,    evacuate    and    recharge refrigerating system (para 6-28, 29, 30). e. Flushing  The  System.    After  compressor motor burnout, flush the system as described below: (1) Refrigerant-11,  along  with  a  small  amount of dry nitrogen to force the refrigerant through the tubing, is recommended for flushing the system. (2) Remove   the   dehydrator   as   described   in paragraph 5-31. (3) Flush  the  refrigerant  tubing  to  remove  all contaminants. (4) The   liquid   line   bypass   and   the   hot   gas bypass   valves   are   normally   open   when   deenergized. These    valves    must    be    open    to    allow    the    flushing refrigerant to flow through the tubing. 6-27. Compressor Crankcase Heater a. General.          The     compressor     crankcase heater   is   designed   to   prevent   refrigerant   sludging.      It ,provides   heat   to   prevent   sludging   and   oil   pumping problems    when    the    compressor    is    exposed    to    low ambient    temperatures.        It    is    a    208    volt,    120    watt resistance  heater  enclosed  within  tubing  and  protected by a thermally insulated cover. b. Removal.    Refer  to  paragraph  5-24,  and remove   the   compressor.      Refer   to   figure   6-12   and remove the crankcase heater. c. Installation.  Replace defective heater and install in reverse order of removal as illustrated in figure 6-12.          Refer     to     paragraph     524,     and     install     the compressor. Test, evacuate and recharge the refrigerant system (para 6-28, 29, 30). 6-15

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