Brochure

Moisture
Water or moisture is always
present in refrigeration sys-
tems, especially with the use
of hygroscopic polyolester (POE) lubri-
cants. Acceptable limits vary from one
unit to another and from one refrigerant
to another. Moisture is harmful even if
“freeze-ups” do not occur. Moisture is
an important factor in the formation of
acids, sludge, copper plating, and corro-
sion. To be safe and sure, keep the mois-
ture level as low as possible.
dirt
Dirt, oxide, scale,
sludges, flux, and
metallic particles
are frequently found in refrigeration
systems. Numerous metallic
contaminants — cast iron dust,
rust, scale, steel, copper, and brass
chips — can damage cylinder walls,
bearings, and plug capillary tubes or
thermostatic expansion valve screens.
In addition to mechanical damage and
“plug-ups,” these contaminants catalyze
chemical reactions that contribute
to decomposition of the
refrigerant-lubricant mixture
at elevated temperatures.
acids
Refrigerants by themselves
are very stable, even when heated to a
high temperature. However under some
conditions, reactions do occur which
can result in the formation of acids. For
example, Refrigerant 22 will decompose
at high temperatures to form hydrochlo-
ric acid where an “acid acceptor” such
as electrical insulation paper is present.
The reaction of refrigerants with water
may cause hydrolysis and the formation
of hydrochloric and hydrofluoric acids.
These acids are usually present as a gas
in the system and are highly corrosive.
In ordinary usage this reaction is negli-
gible, but in a very wet system operating
at abnormally high temperatures, some
hydrolysis may occur.
All of these reactions are increased by
elevated temperature and are catalytic
in effect, resulting in the formation of
corrosive compounds.
Another significant source of acidity
in refrigeration systems is organic acid
formed from lubricant breakdown. Acid
is formed when POE lubricant reacts
with moisture. Appreciable amounts of
organic acid are found in lubricant sam-
ples analyzed in our laboratory. Since
acids corrode metals in a system, they
must be removed.
sludge
and varnish
Although the utmost pre-caution may
be taken in the design and fabrica tion of
a system, once in operation, unusually
high discharge temperatures will cause
the lubricant to breakdown. By-products
of mineral/alkylbenzene lubricant
decomposition are varnish, sludge, and
possibly carbonaceous powder.
Temperatures may vary in different
makes of compressors and under dif-
ferent operating conditions. While tem-
peratures of 265°F/129°C are not unusual
at the discharge valve under normal
operation, temperatures well above
300°F/149°C frequently occur under
unusual conditions. Common sources
of high temperatures in refrigeration
systems are dirty condensers, non-
condensible gases in the condenser, high
compression ratio, high superheat of
suction gas returned to compressor, fan
failure on forced convection condensers,
and others.
In addition to high discharge tempera-
tures, there are certain catalytic metals
that contribute to the lubricant-refriger-
ant mixture breakdown. The most noted
of these in a refrigeration system is iron.
It is used in one form or another in all
systems and is an active catalyst. Copper
is in the same category as iron, but its
action is slower. However, the end result
is the same. This reaction causes sludge
formation and other corrosive materials
that will hinder the normal operation of
compressor valves and control devices.
In addition, air in a system will acceler-
ate the deterioration of the lubricant.
Why Chemical Breakdown Occurs
Page 4 – Bulletin 40-10