Ingersoll-Rand Thermo King CRR DF MPC2000, Maintenance Manual

Page: 121 / 165

Refrigeration Maintenance and Service Operations
120
Pressure Rise Test
Evacuate the system and close valve V1. With valves V3 and V4 open, the pump is isolated and the
system is held under a vacuum. If the Micron Meter rises, one of the following conditions exist.
Leak:
Watch the movement of the Micron Meter needle. If the needle continues to rise until it reaches
atmospheric pressure, it is an indication that a leak exists somewhere in the system. When a leak is in a
system, the vacuum will eventually stabilize at atmospheric pressure.
Moisture:
When the needle indicates a rise and then stabilizes at a level below atmospheric pressure, it is
an indication that the system is vacuum tight, but is still wet and requires additional dehydration and
pumping time (see “Pressure Rise Test Evaluation” below).
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 influence 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 1/4 inch diameter hose as it does through a 1/2 inch
diameter hose. It takes twice as long to pull a vacuum through a 6 foot long hose as it does through a 3
foot long hose.
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
Figure 39: Constant Pressure Rise After Evacuation Indicates System Leak