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TM5-4120-376-14 5-14.  PRESSURE  TESTING.   Pressure   testing   the   refrigeration   system   is   an   important diagnostic  procedure  which  you  should  perform  whenever  the  system  has  been  newly  recharged after  replacement  of  a  component  or  when  the  air  conditioner  is  operating  inefficiently. Pressure  testing  is  accomplished  by  connecting  individual  pressure  gauges  or  a  refrigeration manifold  gauge  to  the  suction  and  discharge  service  valves.  Compare  readings  to  Table  5-2. a.  Set  Up.  Prepare  the  air  conditioner  for  pressure-testing  as  stated  below. (1)   Make   sure   that   the   fresh   air   damper   is   completely   closed   and   that   the   evaporator louver  (inlet)  and  evaporator  (discharge)  are  fully  open. (2)  Hang  an  accurate  thermometer  directly  in  front  of  the  evaporator  louver  (inlet)  to record   dry   bulb   return   air   temperature   to   the   unit. (3)  Hang  an  accurate  thermometer  directly  in  front  of  the  condenser  coil  guard,  making sure  that  the  thermometer  is  shaded  from  direct  sun  light,  to  record  “outdoor  ambient temperature”. (4)  Connect  a  refrigeration  service  manifold  gauge  to  the  suction  and  discharge  service valves,  purging  the  manifold  of  any  air  trapped  in  the  lines. (5)   If   indoor   ambient   temperature   is   too   low,   provide   a   space   heater   to   raise   the   dry   bulb return  air  temperature  to  80°F  (27°C). b.   Procedure.   Perform   the   pressure   test   in   the   following   manner: (1)  Turn  the  mode  selector  to  COOL,  and  the  temperature  selector  to  maximum COOLER. (2)   Slowly   open   the   suction   and   discharge   service   valves   to   which   pressure   gauges   have been   connected. (3)  Let  the  air  conditioner  operate  for  at  least  15  minutes  in  the  cooling  mode,  so  that  all parts  of  the  system  are  stabilized. (4)  Record  the  temperatures  indicated  by  both  thermometers  and  the  pressures  indicated by   both   pressure   gauges. (5)   Compare   the   readings   obtained   from   pressure   testing   with   the   normal   ranges   shown   in Table   5-2. c.   Analysis   of   Discrepancies.   If   actual   pressure-temperature   relationships   differ   from   those shown  in  Table  5-2,  consider  the  following  reasons,  and  take  appropriate  action. (1)  If  pressures  are  too  low:    Check   leaks   in   accordance   with   paragraph   5-11.   Repair   and recharge   the   system   in   accordance   with   paragraph   5-13   and   repeat   the   pressure   test   paragraph 5-14. (2)   If   pressures   are   too   high:   Close  the  suction  service  valve,  remove  the  pressure  gauge, and  bleed  off  the  appropriate  amount  of  refrigerant  in  accordance  with  Table  5-2.  Repeat  the pressure  test  5-14. 5-18

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