10-2014 gForce User Manual ● 39
5.3.2.2 Variable Capacity Compressor
At this point, the unit and compressor will need to be started. Use the VFD “Hand on”
key (7.5.1 Local Control for Charging) of the VFD controller to adjust the speed of the
compressor to minimum frequency. Make sure to set the airflow of the unit to its full
capacity.
NOTE:
A quick and easy way to run the fans and compressor is by using
the manual slide switches provided by the Manual Override Module (3.12
Manual Override Switches). Switch the fan and compressor manual
switches to the ON position. All automatic control is disabled but safety
switches will remain functional.
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.
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.
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