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TM 5-4120-287-15 heating  capacity  of  35,000  BTU/hr  (10.5  kw  (kilowatts)).    The  air  conditioning  unit  is  contained  in  a  single  enclosure  of compact  sturdy  construction  built  to  rigid  military  specifications  and  standards.    The  enclosure  is  subdivided  into  a condenser  section  and  evaporator  section.    The  condenser  section  contains  the  compressor,  condenser  fan,  and  high- pressure refrigerant controls.  The evaporator section contains the evaporator, evaporator fan, expansion valve, heaters, electrical controls, and temperature controls.  Functionally, the air conditioning unit consists of a cooling subsystem and a heating subsystem regulated by either automatic or manual controls from a remote control box. b.    Electrical  Tray  Assembly.    The  electrical  tray  assembly  (fig  1-3)  contains  the  electrical  power  controls  and relays.    The  front  panel  of  the  electrical  tray  assembly  contains  the  circuit  breaker,  the  system  reset  push  button,  the hourmeter, the control circuit fuse, the main power connector, and the remote control box assemble connector.  Mounted within the electrical tray assembly are the motor control relays, the temperature control relays, the transformer, the phase sequence  relay,  and  the  rectifier.    The  28-vdc    (volts  direct  current)  power  required  for  the  operation  of  the  relays  is obtained from the transformer and the rectifier. c.  Remote Control Box Assembly.  The remote control box assembly (fig 1-1) contains the operating controls for the air conditioning unit.  Mounted on the front panel is a four-position (HEAT, OFF, VENT, COOL) five-deck switch and a temperature control variable resistor (minimum setting COOL; maximum setting HEAT).  The rheostat dial is continuously variable between the COOL and WARM positions, which corresponds to a return air temperature range of 60F to 90F. d.    Motor-compressor.    The  motor  compressor  (fig  1-4)  consists  of  positive-displacement  compressor  which  is directly driven by an integral 8-hp, 416-volt, 400-cycle, 3-phase, 4-wire induction motor with a designed speed of 7700 rpm. The  compressor  draws  low  pressure  refrigerant  vapor  from  the  evaporator  and  compresses  it  to  a  high  pressure,  high temperature refrigerant vapor.  The motor-compressor runs continuously when the air conditioner is operating in the COOL mode. e.  Thermostat.   The thermostat (fig 1-3) is located in the evaporator compartment.  The thermostat senses the temperature of the air entering the evaporator and provides control signals to maintain desired temperatures. f.  High-low Pressure Cut-out Switch.   The high-low pressure cutout switch (fig 1-4) is a dual  single  pole,  single throw switch which projects the cooling system from excessive compressor discharge pressure and low compressor inlet pressure.  The high-pressure side of the switch is connected into the compressor discharge line; the low pressure side into the  compressor  inlet  line.    The  switch  has  a  rating  of  2  amperes  at  28  vdc.    The  high  pressure  side  is  set  to  close  the switch  (energizing  the  trip  relay,  which  removes  power  from  the  compressor)  when  the  pressure  in  the  compressor discharge line increases to 260 to 265 psig (pounds per square inch gage).  The switch will automatically reset when the discharge line pressure decreases to 200 to 220 psig.  The low-pressure side is set to close the switch when the pressure in the compressor inlet line decreases to 20 to 21 psig.  The switch will automatically reset when  the  inlet  line  pressure increases to 30 to 40 psig.  The system trip relay is reset by pressing the system RESET switch (fig 1-3). g.  Condenser Fan.  The condenser fan assembly (fig 1-5) provides cooling air for the condenser.  As supplied, it is complete with its own bearings and seals and is permanently lubricated.  The fan is a high-speed (5800 rpm) continuos duty, vane-axle type with a self-contained motor for use on 416-volt, 3-phase, 400-cycle, 4-wire power.  The condenser fan is  rated  at  4120  SCFM  (Standard  Cubic  Feet/Minute).    The  fan  motor  is  constructed  with  an  internal  automatic  reset thermal and overcurrent protector. Note The condenser fan discharge door must be open when unit is operating in cooling cycle.  A Microswitch, activated by the door, prevents operation of compressor motor and condenser fan motor if door is closed. 1-2

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