CSR-20 & CSR-40, September 1999
Refrigeration System Diagnosis and Service
Evacuation and Cleanup of System
6-11
Evacuation and Cleanup of the
Refrigeration System
Contamination
Whenever contaminants have entered the system, a thorough
clean up is required to prevent damage or loss of compressor.
It is well known by the refrigeration service industry that
the purpose of evacuation is to remove moisture and air from
the refrigeration system before charging with new refrigerant
after a system has been opened. The importance of thorough
evacuation and system preparation cannot be over emphasized.
Even infinitesimal quantities of air or moisture in a system can
cause severe problems.
We know that the presence of moisture, oxygen, and heat
under certain conditions can result in many forms of damage.
Corrosion, sludge, copper plating, oil breakdown, carbon for-
mation, and eventual compressor failure can be caused by
these contaminants.
Things that will contaminate a system are (in order of
importance):
•
AIR — with oxygen as a contaminant.
Oxygen in the air reacts with the oil. The oil begins to
break down and can eventually lead to carbonization in
the compressor and acid buildup. The longer this break-
down process goes on, the darker the compressor oil
becomes until finally the color is BLACK indicating
major system contamination.
•
MOISTURE. Moisture in a system will cause metal cor-
rosion and metal plating. It can freeze in the expansion
valve and cause intermittent operational problems. It
reacts in the oil to begin acid buildup.
•
DIRT, DUST, METAL PARTICLES, OTHER FOREIGN
MATERIALS. Particles of any kind left to float through
the system will cause severe damage to all close tolerance
items. Do not leave a system open to the infiltration of
dirt. If you must open a system for any reason, seal off
the open areas as soon as possible and DO NOT work in a
dirty environment.
•
ACID. Air and moisture cause a chemical breakdown of
the oil and/or the refrigerant itself. The acid will acceler-
ate the deterioration of the softer metals (i.e., copper) and
cause metal plating as the softer material begins to cover
the inside of the system. If this condition is not stopped, it
can result in the total destruction of your equipment.
Compressor Oil Color Code
BLACK OIL — indicates carbonization caused by air in the
system.
BROWN OIL — indicates copper plating caused by moisture
in the system.
GRAY OR METALLIC OIL — indicates bearing wear or pis-
ton scoring.
NOTE: If the compressor oil is discolored, perform a
compressor oil acid test (oil test kit P/N 203-457). If
the compressor oil shows an acid condition, change
the oil, the in-line oil filter, the filter drier and perform
a refrigeration system cleanup.
Unit Preparation and Hookup
CAUTION: Do not attempt to evacuate a unit until it
is certain that the unit is leak free. A unit with less
than a full charge of refrigerant should be thoroughly
leak tested. Any leaks found must be repaired.
1.
Recover all refrigerants from the unit and reduce the unit
pressure to the proper level (US Federal Law requires a
-17 to -34 kPa, -0.17 to -0.34 bar, 5 to 10 in.vacuum that
is dependent upon the recovery equipment used).
2.
Break vacuum with refrigerant and equalize system pres-
sure to 0 kPa, 0 bar, 0 psig. Replace the liquid line filter
drier if necessary.
NOTE: Hermetic units feature a large, one-piece
filter drier/in-line filter. The filter drier should not
require replacement unless major system conta-
mination requires evacuation and cleanup of the
refrigeration system.
3.
Confirm that the Evacuation Station functions properly
and determine “Blank Off” Pressure. The Blank Off
Pressure of the Vacuum Pump is the deepest vacuum that
the vacuum pump can attain when isolated from the rest of
the system.
If a vacuum pump (isolated from a system) is started
and the Micron Meter responds quickly by going to a deep
vacuum, the operator can be confident that the pump and
oil are in good condition. If the vacuum pump fails to
reach a deep vacuum within 5 minutes, the operator should
suspect the condition of the oil or the pump. Thermo King
recommends that the pump oil be changed first to see if the
rate of reaching a deep vacuum is improved.
