Thermo King 098916, Maintenance Manual

Page: 140 / 196

Refrigeration Maintenance
139
Unit Evacuation
1. Turn on the vacuum pump. Open the gas
ballast valve located on top of the pump
housing behind the handle (the valve is fully
open at two turns counterclockwise). Evacuate
the system to 500 microns to achieve a final
equilibrium pressure of 2000 microns or less.
The final equilibrium pressure is determined
with the Thermo King Evacuation Station
using the following procedure (called a
pressure rise test):
a. Evacuate the system using the evacuation
station until the vacuum level reaches
1000 microns. Then close the gas ballast
valve.
b. Continue evacuation to 500 microns or
until vacuum stabilizes at its lowest level.
Contamination may delay reaching the
lowest level for a period of several hours
or more.
c. Close valve V1 to isolate the vacuum
pump from the system.
d. Observe the vacuum level on the micron
meter.
When the meter has stabilized, the value indicated
on the micron meter is the equilibrium pressure.
This reading must be 2000 microns or less.
NOTE: The presence of refrigerant in the
compressor oil may prevent a low vacuum
reading from being achieved. Compressor oil
can continue to outgas for long periods of time.
2. If the vacuum level appears to stall above
500 microns, back seat the discharge service
valve and observe the micron meter.
• 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 5 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 5 minutes, the unit is ready
to charge. See “Charging the System with
Refrigerant”.