october2021 - 13

INDUSTRY EXPERT
COLUMN
a wash tub with a warm water/dishwashing
soap mix. Agitate the washable filters in the
tub to flush out contaminants. If there is a lot
of pollen or large particles on the filter surface,
vacuum this off first. Rinse the filters with
fresh water and set them in fresh air to dry.
Sunlight is a wonderful disinfectant so direct
sun is preferred for drying.
Replaceable filters get replaced per manufacturer
recommendation. Some modern
PCAs can monitor filter pressure drop and
can alert on a human interface display when
it is time to change filters.
Evaporator Coil Cleaning
The evaporator is the component where the
cold air is made, so to speak. It is where heat is
transferred out of the ambient air and into the
refrigerant flowing within the evaporator fins
and tubes. This isn't meant to be a Refrigeration
101 lesson, so simply understand the evaporator
needs to be clean for proper heat transfer.
The best way to keep an evaporator clean
is to never let it get dirty. With proper filter
maintenance, personnel shouldn't need to
worry too much about the evaporator. Evaporators
are not very easily accessed in many
PCA brands as they are trapped inside a sheet
metal plenum. If troubleshooting indicates a
dirty evaporator may be an issue, consult the
manufacturer.
When cleaning an evaporator, a plain water
rinse is usually all that is needed. Very mild
chemicals, meant for evaporator cleaning, can
be used if there are substantial contaminants
on the evaporator fins. Cabin supply air flows
through the evaporator, so strong chemical
cleaning should not be performed.
Heating Elements
Heating functions get verified before each
heating season. Electric elements can be verified
using an ammeter and specified circuit
current values. A thermometer is used to verify
heating discharge temperature. Consult the
manufacturer for heating element cleaning
procedures, if applicable. Year-round heating
regions may require additional checks.
Condensation Pumps
Some PCAs utilize a pump to remove evaporator
condensation from the plenum. Sometimes
the water is pumped right to the ground
beneath the PCA and sometimes local code
requires pumping to a sanitary drain. Be certain
the pump is working as designed. Check
with the PCA manufacturer for suggested
condensation pump winter " layup " procedures.
The pump is checked before cooling
season start-up. Year-round cooling regions
may require additional checks.
Condenser Coil Cleaning
Short of a refrigeration process explanation,
understand that the condenser is an integral
part of the refrigeration system and will not
function efficiently (or at all) if very dirty. Even
a thin layer of oily residue can hinder heat
transfer and harm efficient cooling operations.
Sometimes a plain water rinse is enough for
cleaning a condenser coil. Condensers at an
airport get contaminated with exhaust from
aircraft and ground support equipment and
may require chemical cleaning. It is advised
to consult the PCA manufacturer (and/or coil
manufacturer) for the appropriate condenser
coil cleaner to be used.
There are unique materials used by individual
coil manufacturers. Various protective
coil coating products are employed. This
requires a coil manufacturer consultation to
determine what cleaning chemicals are best
for their coils. Unauthorized cleaning products
can damage the condenser and make its
operation worse. Chemical cleaners get mixed
with water, per the chemical manufacturer
directions, and applied as directed. Many of
these cleaners use a foaming action to drive
out contaminants from deep within the coil
fins or channels. Consult the manufacturer to
determine if using warm water can improve
this process. Be certain to rinse off the chemical
completely and only leave it on for the
recommended amount of time.
When cleaning the condenser coil, also
clean the condenser fan blades with a freshwater
rinse. Be careful not to spray water
directly at bearings or any openings in the
condenser fan motor. Some local environmental
codes require the capture of rinsing
water. Condenser cleaning is performed before
the cooling season. In a year-round cooling
region, or in an exceptionally dirty environment,
more cleanings may be advised. Consult
the equipment manufacturer and use their
recommendations as the minimum standard.
Conclusion
A temperate aircraft cabin is necessary for
a variety of reasons. Always use the factory
suggested maintenance tasks and intervals
as a minimum standard. Technicians
with advanced HVACR skills may wish to
go beyond factory minimum maintenance
recommendations.
Cleaning and/or replacing filters is one of
the most important things a technician can
do regarding PCA maintenance. Keeping
evaporator and condenser coils clean is also
a very important aspect as these components
are designed to transfer heat and they perform
better when clean.
Electrical checks are important for human
as well as machine health and safety. Equipment
mechanical components should be evaluated,
and hardware tightened to specification.
Hose and connector condition, though
often overlooked, is extremely important for
proper PCA operations. Clean, leak-free hoses
support good cabin air quality.
A final operational evaluation and discharge
air temperature check can verify
satisfactory operations. Aircraft need to be
supplied with adequate air volume and temperature
while on the ground. A well maintained
PCA will provide these needs.
This article continues online with
comprehensive maintenance details
to ensure electrical and mechanical
integrity, tips on general cleaning,
strategies for cleaning hoses
and connectors and additional
information regarding operational
checks.
Visit AviationPros.com/21238251 to
read the article in its entirety.
ABOUT THE AUTHOR:
Tim Fox is a facilities engineering and maintenance projects and programs manager
at United Airlines. He has been employed at United Airlines for 32 years and has
been an HVACR practitioner for 36 years. He serves as United Airlines' subject matter
expert for aircraft pre-conditioned air equipment and facility HVACR matters. He can
be reached at timothy.fox@united.com
OCTOBER 2021 AviationPros.com 13
http://www.AviationPros.com/21238251 http://www.AviationPros.com
october2021

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