Thermo King 920000, Manual

Page: 107 / 190

Refrigeration Maintenance
107
5. Observe the receiver tank sight glass and the
unit’s discharge pressure.
6. By the time the discharge pressure drops
approximately 50 psi (345 kPa), the ball in the
receiver tank sight glass should begin to move
and the liquid level should drop.
a. When discharge pressure stabilizes, the
ball and liquid level will rise.
b. If the ball will not begin to move or if the
liquid level will not drop, the unit most
likely has an overcharge of refrigerant.
The refrigerant level should be adjusted.
Adjusting the Refrigerant Level
1. Stop the unit and remove some refrigerant
with an approved refrigerant recovery device.
2. Perform a refrigerant level check and repeat
the overcharge test.
3. If the liquid level is low, add refrigerant as
follows:
a. Connect a refrigerant tank to the gauge
manifold service line and purge the line.
b. Mid seat the compressor suction service
valve.
c. Set the refrigerant tank for liquid removal
and open the hand valve.
d. Operate the condensing unit in high speed
with both evaporators in Cool.
e. Observe the suction pressure and slowly
open the gauge manifold low pressure
hand valve to allow liquid refrigerant to
flow into the compressor suction service
valve.
f. Control the liquid flow so the suction
pressure increases approximately 20 psi
(138 kPa).
g. Maintain a discharge pressure of at least
275 psi (1896 kPa) while adding
refrigerant.
h. Close the hand valve on the refrigerant
tank when the liquid level approaches the
top of the receiver sight glass.
4. Repeat the overcharge test.
Moisture Indicating Sight
Glasses
The receiver tank is equipped with a moisture
indicating sight glass. The outer edge of the sight
glass has a colored ring approximately 0.1 in.
(2.5 mm) thick. The color of the ring indicates the
moisture content of the refrigerant, but it may not
be completely reliable.
Green = Dry
Chartreuse = Caution
Yellow = Wet
A system has to run for at least 15 minutes to
change the color of the indicator ring after the
moisture content of the system has been changed.
For example, evacuating a system to remove the
moisture will not change the color of the indicator
ring until the system has been recharged and then
operated for at least 15 minutes.
Refrigerant Leaks
Use a reliable leak detector (e.g., electronic
detector or soap bubbles) to leak test the
refrigeration system. Inspect for signs of oil
leakage which is the first sign of a leak in the
refrigeration system.
1. Floating Ball
2. Colored Ring
Figure 57: Moisture Indicating Sight Glasses
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