AAON M2 Series Installation Operation & Maintenance Download

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Indoor Coils

Indoor  cooling/evaporator  coils  must  be
cleaned regularly to maintain unit efficiency
and  operation.    Dirty  evaporator  coils  will
eventually  freeze  up  and  often  result  in  a
time  consuming  and  expensive  service  call.
Clean  filters  will  help  to  prevent  dirt  from
accumulating  on  cooling  coils,  however
cooling  coils  should  be  cleaned  at  least
annually by an HVAC professional.

Refrigeration Cycle

Satisfactory performance of the refrigeration
cycle  can  be  determined  by  measuring
suction line superheat.  In order to determine
if refrigerant flowing from the evaporator is
dry,  ensure  that  the  system  has  enough
refrigerant to produce liquid line subcooling,
but  not  so  much  to  cause  abnormally  high
condensing  temperatures  (and  pressures).
Refrigerant cycle analysis is best performed
in  conditions  that  approach  the  conditions
where the air conditioner will be expected to
operate.

Brazed Plate Heat Exchanger Cleaning

Because  of  a  normally  high  degree  of
turbulence  in  brazed  plate  heat  exchangers,
for  many  applications  the  heat  exchanger
channels are self-cleaning.  For applications
that  are  not  self-cleaning  (i.e.  hard  water  at
high  temperatures,  etc.)  or  applications
where  additional  cleaning  is  desired,  it  is
possible  to  clean  the  brazed  plate  heat
exchanger by circulating a cleaning liquid.

Use  a  tank  with  weak  acid,  5%  phosphoric
acid  (H3PO4)  or,  if  the  exchanger  is
frequently

cleaned,

oxalic

acid

(H2C2O4).    Pump  the  cleaning  liquid
through  the  exchanger.    For  optimum
cleaning,  the  cleaning  solution  flow  rate
should  be  a  minimum  of  1.5  times  the
normal  flow rate, preferably in  a back-flush
mode.    After  cleaning,  the  heat  exchanger
must be rinsed with clean water.  A solution
of  1-2%  sodium  hydroxide  (NaOH)  or
sodium bicarbonate (NaHCO) before the last
rinse ensures that all acid is neutralized.

E-Coated Coil Cleaning

Documented  routine  cleaning  of  e-coated
coils  is  required  to  maintain  coating
warranty coverage.

Surface  loaded  fibers  or  dirt  should  be
removed  prior  to  water  rinse  to  prevent
restriction of airflow. If unable to back wash
the  side  of  the  coil  opposite  of  the  coils
entering  air  side,  then  surface  loaded  fibers
or  dirt  should  be  removed  with  a  vacuum
cleaner. If a vacuum cleaner is not available,
a

soft non-metallic

bristle brush may be

used.  In  either  case,  the  tool  should  be
applied  in  the  direction  of  the  fins.  Coil
surfaces  can  be  easily  damaged  (fin  edges
bent  over)  if  the  tool  is  applied  across  the
fins.

Use  of  a  water  stream,  such  as  a  garden
hose, against a surface loaded coil will drive
the  fibers  and  dirt  into  the  coil.  This  will
make cleaning efforts more difficult. Surface
loaded  fibers  must  be  completely  removed
prior to using low velocity clean water rinse.

A

monthly

clean

water

rinse

recommended for coils that are applied in
coastal or industrial environments to help to
remove chlorides, dirt, and debris. It is very
important

when

rinsing,

that

water

temperature  is  less  than  130°F  and  pressure
is  than  100  psig  to  avoid  damaging  the  fin
edges. An elevated water temperature (not to
exceed  130°F)  will  reduce  surface  tension,
increasing  the  ability  to  remove  chlorides
and dirt.

Electric  shock  hazard.  Shut  off  all
electrical  power  to  the  unit  to  avoid
shock  hazard  or  injury  from  rotating
parts.

WARNING