Thermo King CRR-40 119, Manual

Page: 134 / 170

Refrigeration Maintenance and Service Operations
134
• A drop in pressure indicates that the
compressor oil is out-gassing and further
evacuation is necessary.
• An increase in pressure indicates that a
leak exists or there is moisture in the
system. Perform a “Pressure Rise Test”
and evaluate.
3. Close valve V1 when the desired vacuum
level has been
reached.
4. Wait five minutes and read the Micron Meter.
• A system that is leak free and dry will
remain below 2000 microns for five
minutes.
• A system that rises above 2000 microns
but stabilizes below atmospheric pressure
is probably contaminated with moisture or
has refrigerant out-gassing from the
compressor oil. Additional evacuation is
required.
• A system that continues to rise without
stabilizing has a leak and must be repaired.
5. If the vacuum level remained below 2000
microns for five minutes, the unit is ready to
charge.
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 (see graph, “Constant
Pressure Rise After Evacuation Indicates
System Leak”, below).
• 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 graph, “Pressure Rise Levels Off
After Evacuation Indicates Moisture in
System”, 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
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 45: Constant Pressure Rise after Evacuation
Indicates System Leak
AJA1318