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TM 5-4120-270-15 densation.  A system of solenoid and expansion  valves directs  the   liquid   refrigerant   to   the   evaporator   coil   for conditioned area cooling. When the desired temperature  is  attained,  the  same  valves    bypass  the evaporator    coil    to    prevent    further        cooling    of    the conditioned area. The compressor operates continuously whenever the selector  switch is on "COOL" to prevent voltage fluctuations in the power line.  A time delay  relay  keeps    the  hot  gas  bypass  valve  open  and prevents  operation  of  the  compressor  for  30  seconds after  initial startup. Note.    Hot  gas  bypass  solenoid  valve  V,  remains  at    all time during cooling cycle and bypass cycle operation.  It opens   when   selector   switch   is   moved   from   "COOL" position  ad  remains  open  for  30  seconds  after  selector switch  is returned to "COOL" position. c. Cooling   Cycle   of   Operation.      When   the conditioned area temperature rises above the temperature control thermostat setting, a set of contacts opens, permitting liquid line solenoid valve V,  to return to its normally open position.  Liquid  refrigerant is metered to  the  evaporator  coil  by    thermal  expansion  valve  W1. Thermal expansion  valve W, bypasses a small  amount of   liquid   refrigerant   to   the   suction   line   to   maintain   a constant  load  on  the  compressor.    The  back  pressure ,regulating  valve  (BPR)  prevents  evaporator  coil    icing and   loss   of   efficiency.      The   condenser   receiver   and accumulators further stabilize the  system. d. Bypass   Cycle   of   Operation.      When   the conditioned area temperature falls below the temperature control thermostat setting, a set of contacts closes,  energizing  the  pull-in  coil  of  liquid    line  solenoid valve V, and blocking the flow of  liquid refrigerant to the evaporator  coil.    Suction    pressure  increases  and  the back  pressure  regulating  valve  (BPR)  opens  to  bypass hot refrigerant gas to the suction line.  At the same time, thermal expansion valve W, meters increased  amounts of  liquid  refrigerant  into  the  suction    line  to  maintain  a constant    load    on    the    compressor.        The    condenser receiver and accumulators  further stabilize the system. e. Heating   Operation.      Placing   the   selector switch  in  the  "LO  HEAT"  position  actuates  half    of  the evaporator    heaters    mounted    in    the    conditioned    air stream,  directly  behind  the  evaporator    coil.    When  the selector switch is placed in the  "HI HEAT" position, the remaining  heaters  are    energized,  providing  maximum heating capacity. 5-17. Cover Panel a. Removal.    Refer  ’to  figure  3-8  and  remove cover panel. b. Installation.  Refer to figure M8    and  install cover panel. 5-18. Control Panel a. Removal.    Refer  to  figure  5-2  and  remove control panel. Note.  Use care in removing temperature control thermostat remote bulb and capillary tubing. b. Installation.    Refer  to  figure  5-2  and  install’ control panel. 5-19. Junction Box a. Removal.        Refer    to    figure    5-2    and remove junction box. b. Installation.      Refer   to   figure   5-2   and install junction box. 5-20. Electrical Heaters and High Temperature Cutout a. Removal.        Refer    to    figure    5-8    and remove electrical heaters and high temperature cutout. b. Installation.        Refer    to    figure    58    and install electric heaters and high temperature cutout. 5-21. Evaporator Fan Motor a. Removal.      Refer   to   figure   3-15   and   remove evaporator fan motor. b. Installation,.      Refer   to   figure   315   and   install evaporator fan motor. 5-22. Sight Glass a.  Removal.  Refer to figure 54 and remove sight glass. b.  Installation.  Refer to figure 5-4 and install sight glass. 5-23. Evaporator Coil a. Removal.        Refer    to    figure    55    and    remove evaporator coil. b. Installation.        Refer    to    figure    55    and    install evaporator coil. 5-24. Compressor a. Removal.        Refer    to    figure    56    and    remove compressor. b. Installation.        Refer    to    figure    -6    and    install compressor. 5-25. Expansion Valves a. Removal.        Refer    to    figure    5-7    and    remove expansion valves. Note. Use   care   in   removing   remote   sensing bulb and capillary tubing. 5-4

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