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Evacuation and Cleanup of System
Refrigeration System Diagnosis and Service
CSR-20 & CSR-40, September 1999
Factors Affecting the Speed of System Evacuation
It is almost impossible to state the exact amount of time
required to evacuate any system. Some factors that can influ-
ence evacuation time are listed below.
• System size
• Amount of moisture contained in the system
• Ambient temperature
• Internal restrictions within the system
• External restrictions between the system and the vacuum
pump
Hose size, both diameter and length, affect evacuation
times. Laboratory tests show that the evacuation time can be
significantly reduced by larger diameter hoses and shorter
hoses. To obtain optimum pumping speed, keep hoses as short
as possible and as large in diameter as possible. For example,
it takes eight times as long to pull a given vacuum through a 6
mm (0.25 in.) diameter hose as it does through a 13 mm (0.5
in.) diameter hose. It takes twice as long to pull a vacuum
through a 2 meter (6 ft) long hose as it does through a 1 meter
(3 ft) long hose.
Heat Saves Time
A useful and practical time saver is the application of heat to
the system. Increasing the temperature of the compressor oil
and refrigerant will speed up the vaporization of any water
present in the system.
WARNING: Never use a torch or other concentrated
heat source to heat the compressor or other refriger-
ation system component.
Heat lamps, electric heaters, or fans can be applied to the
compressor crankcase and other parts of the system to increase
the temperature of the refrigerant and compressor oil.
Pressure Rise Levels Off After Evacuation Indicates
Moisture in System
1. Close the vacuum valve and watch the movement of
vacuum gauge needle. If needle shows a pressure
rise but finally levels off to a constant pressure, the
system still contains too much moisture.
Dehydration and additional evacuation time are
required.
2. Time
3. Pressure (Vacuum)
4. Atmospheric Pressure
Constant Pressure Rise After Evacuation Indicates
System Leak
1. Close the vacuum valve and watch the movement of
vacuum gauge needle. If needle continues to rise,
this is an indication that a leak exists in the unit or
connecting line. The leak must then be located and
eliminated.
2. Time
3. Pressure (Vacuum)
4. Atmospheric Pressure
