Installation, Operation and Maintenance Manual
4.1.2 Split Air-Cooled Systems Charging (Units with Indoor Condenser or Outdoor Condenser)
After refrigerant piping installation, pressure test, and vacuum procedure is properly is complete, connect the
refrigerant manifold gauge set and make sure the manifold gauge set is properly purged. Systems with R-410A
require approximately 3 lbs. per nominal ton.
For example, a model GPAX-0334 is a nominal 3-ton unit. Charge with about 9 lbs. if R-410A. It is likely that more
refrigerant will be required to complete the charging procedure for additional piping between the evaporator and
the condenser. After hoses are properly purged, from a vacuum, slowly open the high side liquid line valve on the
refrigerant manifold gauge to feed liquid refrigerant through the high side of the system until the pressures
equalizes. At this point there will be about 70 to 80% of the total charge in the system. Use recovery machine to
add refrigerant if necessary.
WARNING Before starting a compressor, the crankcase heater should be
energized for a minimum of 12 hours to reduce the possibility of liquid slugging
on start-up. Failure to energize the crankcase heater could result in compressor
damage. If the system is charged from a vacuum, the preheating of the
compressor is not necessary.
Start the evaporator fan and compressor. 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 and can be caused by flashing from liquid line pressure drop,
low sub-cooling or low charge. It is likely more refrigerant will be required to complete the charging procedure.
Finish charging by slowly opening the valve on the refrigerant manifold set to meter liquid refrigerant into the low
side of the system.
Adjust the refrigerant charge until the sub-cooling is 8°F to 10°F and has sparse bubbles. The unit should be allowed
to stabilize for several minutes before meaningful measurements can be taken.
A properly charged R410A system operating at typical parameters will have the following pressures:
Typical Operating Parameters
Superheat (at the compressor suction line)
NOTICE Charging to a full liquid line sight-glass should never be the sole means
of determining the correct refrigerant charge. Finish charging by slowly
opening the valve on the refrigerant manifold set to meter liquid refrigerant
into the low side of the system. 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.
When charging is complete, add the correct amount of oil, if the line run exceeds more than 66 feet (20m). This
procedure must be conducted with the system running at high load (compressor at full speed).
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