Refrigeration Maintenance
182
Evacuation and Cleanup of the Refrigeration System
A thorough clean up is required whenever contaminants have entered the system. This will prevent
damage to the compressor.
The purpose of evacuation is to remove moisture and air from the refrigeration system after a system has
been opened to the atmosphere. Evacuation must occur before recharging a system with new refrigerant.
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.
The presence of moisture, oxygen, and heat can create many forms of damage. They can create corrosion,
sludge, copper plating, oil breakdown, carbon formation, and eventual compressor failure.
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 breakdown
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 corrosion 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
accelerate 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.
Unit Preparation and Hookup
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 pressure to 0 kPa, 0 bar, 0 psig. Replace the liquid
line filter drier if necessary.
NOTE: Replace the one-piece filter drier when major system contamination requires evacuation
and cleanup of the refrigeration system.
3. Confirm that the evacuation station functions properly. 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. The operator can be confident that the pump and oil are in good
condition, if a vacuum pump (isolated from a system) is started and the micron meter responds
quickly by going to a deep vacuum. 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. It is recommended that the
pump oil be changed first to see if the rate of reaching a deep vacuum is improved.
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.
Summary of Contents for 098203
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