Refrigeration Maintenance
129
NOTE: If the liquid level in the receiver sight
glass drops during step 4, the unit is not
overcharged and it is not necessary to
complete the procedure.
5. Remove the condenser cover to rapidly reduce
discharge pressure.
6. Observe the receiver tank sight glass and the
unit discharge pressure.
7. By the time the discharge pressure drops
approximately 50 psig (345 kPa), the liquid
level in the receiver tank should drop.
a. When the discharge pressure stabilizes,
the liquid level will rise.
b. If the liquid level will not drop, the unit
most likely has an overcharge of
refrigerant. The refrigerant level should be
adjusted.
To adjust 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 unit in high speed 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 psig
(138 kPa).
g. Maintain a discharge pressure of at least
275 psig (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 Glass
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 is not
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 that is suitable for
R-404A to leak test the refrigeration system.
Inspect for signs of oil leakage, which is the first
sign of a leak in the refrigeration system.
NOTE: It is normal for compressor shaft seals to
have a slightly oily film.
1.
Floating Ball
2.
Colored Ring
Figure 209: Moisture Indicating Sight Glass
AEA672
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