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Figure 1-10  Installation and base plan.
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TM-5-4120-287-15 Air Conditioner Base Mounted 208V 3 Phase Manual
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Theory (fig. 1-11)
TM 5-412-287-15 Section III. THEORY OF OPERATION 1-5. General This section describes the theory of operation of the refrigerant vapor cycle system . 1-6. Theory (fig. 1-11) a. During air conditioning operation, the condenser  fan draws ambient air through the condenser and discharges it through the condenser fan discharge door. The evaporator fan draws air from the compartment to be air conditioned into the  evaporator  section  where  it  is  mixed  with  fresh  air  (if  desired)  and  conditioned;  then  the  air  is  passed  back  into  the compartment through the evaporator conditioned air outlet port. b. Low  pressure,  low  temperature  refrigerant  vapor  (refrigeran-12)  enters  the  compressor  through  the  compressor inlet leading from the evaporator outlet. The refrigerant vapor is compressed to a high pressure and temperature. c. From  the  compressor,  the  refrigerant  vapor  enters  the  condenser,  where  it  is  condensed  into  a  high-pressure liquid by giving up heat to the condenser airstream. The electrically driven  condenser  fan  draws  cooling  air through the condenser and exhausts it to atmosphere. The liquid refrigerant then collects in the receiver, upstream of the condenser. The receiver stores surplus liquid refrigerant and compensates for inequalities in flow rates. d. After leaving the receiver, the liquid refrigerant flows through the subcooler. Subcooling is necessary because of the  line  pressure  drop  in  the  line  leading  to  the  thermo-expansion  valve.    The  subcooler  lowers  the  liquefied  refrigerant temperature    sufficiently  (approximately  8F)  to  preclude  flashback  (vaporization)  of  the  refrigerant  on  the  way  to  the thermo-expansion valve. e. From  the  subcooler,  the  liquid  refrigerant  passes  through  the  filter-drier.  The  liquid  refrigerant  upon  entering  the filter-drier is directed through the drying agent and the filterscreen. f. From  the  filter-drier,  the  liquid  refrigerant  flows  to  the  solenoid  valve.  The  remote  thermostat,  which  senses compartment temperature, controls the operation of the solenoid valve. The valve closes to stop the flow of refrigerant to the expansion valve when compartment  cooling is not required.  When the solenoid valve is closed, pressure in line from the evaporator to the compressor drops because the compressor is still operating.  When this pressure drops to 35 to 37 psig, the hot gas bypass valve opens permitting compressor discharge vapor to flow into the compressor inlet line. When the  temperature  in  the  compressor  inlet  line  becomes  excessive  due  to  hot    bypassed    vapor,  the    liquid  quench  valve opens to permit high-pressure liquid refrigerant to vaporize and  flow into the line; thereby de-superheating the bypassed vapor and reducing the line temperature to a safe superheat level entering the compressor. g.   The liquid refrigerant passes from the solenoid valve through the refrigerant liquid sight indicator, and enters the inlet port of the thermostatic expansion valve where it is metered by the action of the valve pin. The valve pin is actuated by a diaphragm whose position is determined by the evaporator load and the superheat level sensed by the valve thermal bulb.  To  compensate  for  the  effect  of  pressure  drop  across  the  evaporator,  an  external  pressure  equalizing  line  is connected  between  the  evaporator  outlet  and  the  chamber  below  the  valve  diaphragm.  Thus,  the  true  evaporator  outlet pressure is exerted beneath the valve diaphragm.  The operating pressures on the valve diaphragm are now free from the effect of the pressure drop through the evaporator, and the expansion valve will respond to the superheat of the refrigerant vapor leaving the evaporator. h. The  thermostatic  expansion  valve  is  factory  adjusted  to  maintain  a  nominal  5F  superheat  setting.    The  valve function is to maintain the nominal superheat setting in the evaporator,  as  dictated  by  the  thermal  sensing  bulb.   This  is accomplished by modulating the flow rate of  liquid refrigerant to the evaporator. i. The  actual  cooling  effect  in  this  vapor  cycle  system  occurs  in  the  evaporator  where  the  liquid  refrigerant  is evaporated under re 1-19

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