38 ● gForce Ultra User Manual 10-2014
Check the liquid line sight glass to get a feel for the approximate charge. Bubbles in
the sight glass are not unusual at this point. It is likely more refrigerant will be required
to complete the charging procedure.
If the receiver head pressure is below the required pressure (350 PSIG (2413 kPa) for
R-410A), block part of the condenser coil surface until the pressure rises. During
extremely cold weather all the condenser fan have to be de-energized to maintain head
pressure.
Observe the sight glass on the receiver. Add refrigerant through the suction line until
the level of liquid in the receiver is approximately 1/3 from the bottom (the leveling ball
in the receiver will start to float) of the sight glass. At this point the receiver is 80%
full. Observing the receiver sight glass becomes difficult when they are remote
mounted near the condenser. The system should be allowed to stabilize for 15 to 20
minutes before meaningful measurements can be taken. After the system is allowed to
stabilize, verification of a few key measurements should be noted. Add refrigerant to
the system until the ball in the sight glass at the 1/3 level.
6 to 12°F (3.33 to 6.67°C) Differential
Measure the superheat at the compressor suction line at least 6 inches (152 mm) away
from the compressor.
Remove any blocks that may have been used on the condenser coil. If the ambient
temperature while charging is below 70⁰F (21⁰C), some of the refrigerant will be backed
up in the condenser coil causing the liquid level in the receiver to drop (this is normal).
Note:
Charging to a full liquid line sight glass should never be the sole
means of determining the correct refrigerant charge. Other parameters
such as superheat, suction pressure, head pressure, sub-cooling and
ambient temperature are also important. A system charged to a clear sight
glass is often overcharged.
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