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Page Title: Thermostatic Expansion Valve
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TM 5-412-287-15 1 Conditioned air outlet port   7 Vent air door control knob 2 Heater bank assembly (2)   8 Evaporator blower access panel assembly 3 Electrical tray access panel assembly   9 Evaporator left-side access panel assembly 4 Recirculating air inlet port 10 Remote control harness assembly 5 Recirculating air door 11 Remote control box assembly 6 Fork lift channel (2) 12 Lifting eye (4) Figure 1  Continued. located within the glass viewing window, changes from green to yellow as the system moisture content becomes critical. System moisture content in excess of 15 ppm (parts per million) is considered critical. o. Thermostatic Expansion Valve. (1)  The thermostatic expansion valve (fig. 1-6) is utilized to regulate liquid refrigerant flow to the evaporator.  It is the dividing  point  between  the  high  and  low  pressure  sides  of  the  system.    The  valve  responds  to  the  temperature  of  the refrigerant   vapor   leaving   the   evaporator;   and   regulates   the   amount   of   refrigerant   entering   the   evaporator   in   exact proportion to the rate of evaporation of the liquid refrigerant in the evaporator.  This controlled flow ,prevents the return o f liquid refrigerant to the compressor. (2)  The valve consists of a body flange mounted on the inlet side of the evaporator, a cage assembly, and a power assembly with a remote temperature-sensing bulb which is clamped on the suction line leaving the evaporator.  The power assembly  contains  a  diaphragm,  diaphragm  chamber,  capillary  tube  connection  for  the  remote  bulb,  and  a  port  for  the external equalizing line.  The remote temperature-sensing bulb, capillary tube, and the chamber formed by the diaphragm comprise a closed system which is charged with a volatile fluid.  An external equalizer line is connected to the evaporator outlet.  The cage assembly contains a valve pin and the superheat adjusting spring. p.    Evaporator    Assembly.    The  evaporator  assembly  (fig.  1-7)  consists  of  an  evaporator  cooling  coil  and  refrigerant distributor.  The evaporator is a 13 circuit, direct expansion coil of aluminum fin and copper tube construction.  It removes heat from the air being conditioned by vaporization of the liquid refrigerant flowing through it.  In order to assure efficient use of this multicircuited coil a distributor is used to direct equal amounts of refrigerant to each individual coil circuit.  The unit is of cross-counterflow design with both air and refrigerant flowing in a horizontal plane. q.  Evaporator  Blower.  The evaporator blower (fig. 1-7) directs the air to be conditioned through the evaporator where it is cooled.  As supplied, the evaporator fan is complete with scroll, wheel and inlet rings; and is rated at 1200 SCFM.  It is a medium speed (3750 rpm), double inlet centrifugal blower with a continuous duty direct coupled motor.  The evaporator fan operates on 416-volt, 3-phase, 400-cycle, 4-wire power.  The motor is designed with inherent thermal and over-current protection and  permanently lubricated sealed bearings. r.  Pressure  Relief  Valve.  The pressure relief valve (fig. 1-4) is a straight through  type valve, located in the refrigerant liquid  line,  downstream  from  the  filter-drier.    It  functions  to  protect  the  system  components  from  high  internal  pressure, resulting from possible malfunctions of the system or its components, by discharging the high pressure refrigerant to the atmosphere.    The  valve  consists  of  a  metal  body  which  encloses  a  spring-loaded  piston  assembly.    The  valve  is  set  to relieve at 350 psig internal system pressure. s.    Liquid    Quench    Valve.    The  liquid  quench  valve  (fig.  1-4)  is  utilized  to  prevent  excessive  compressor  inlet temperature during light-load operation when the refrigerant solenoid valve is closed and the hot gas bypass valve is open. The valve, in effect, is a small capacity expansion valve with its sensing bulb mounted to the compressor inlet line.  The valve function is to de-superheat bypassed compressor discharge gas. 1-5

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