22
To test the plug fan modules in manual mode, turn on blower and fan speed switch on manual over-
ride modules. This will enable the fan control signal at approximately 90%. The fans will spin at
near full speed if the contactors are enabled.
Start the evaporator fan and verify the fan rotation. From a vacuum, add liquid refrigerant to the
high side of the system until the pressures equalize. Start the compressor. Check the liquid line
sight glass to get a feel for the approximate charge. Bubbles in the sight glass are not unusual at
thispointandcanbecausedbyashingfromliquidpressuredrop,lowsub-coolingorlowcharge.
It is likely more refrigerant will be required to complete the charging procedure.
If the receiver (head) pressure is below 322 PSIG with R-410A (230 PSIG R-407C), block part of the
condenser coil surface until the pressure rises to 322 PSIG R-410A (230 PSIG R-407C) or higher.
If the receiver (head) pressure is below 322 PSIG with R-410A) (230 PSIG with R-407C), block part
of the condenser coil surface until the pressure rises to 322 PSIG for R-410A (230 PSIG R-407C)
or higher. During extremely cold weather all the condenser fan have to be de-energized to maintain
head pressure. Add refrigerant to the system until the ball in the sight glass at the 1/3 level.
After the system is allowed to stabilize, the superheat at the compressor suction line (reading from a
least 6 inches from the compressor) should be 8-15°F. Units with remote condensing units (DRCU),
the superheat should be 20 to 25
o
F at the compressor.. Remove any blocks that may have been
used on the condenser coil. If the ambient temperature while charging is below 70°F, 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 deter-
mining the correct refrigerant charge. Other parameters such as superheat, suction pres-
sure, head pressure, sub-cooling and ambient temperature are also important. A system
charged to a clear sight glass is often overcharged.
4.3 Water/Glycol System
4.3.1 Water/Glycol Cooled System Charging
All water/glycol cooled units are factory charged with refrigerant. The water regulating valve should
be adjusted to maintain a condensing temperature of 105 - 119
o
F. Saturated suction temperature
should be 33
o
F PSIG or higher. The superheat at the compressor suction line at least 6 inches
away from the compressor should be between 8-15°F.
Field charging of water/glycol systems should be done by referring to the unit’s electrical nameplate.
Thefactorychargeisindicatedonthenameplate.Althoughthisgurerepresentstheinitialfactory
charge, it is still necessary to measure and note proper unit operation including superheat, head and
suction pressure. Some adjustment charge may be required.
Adjust the refrigerant charge until the sight glass clears or has sparse bubbles. The unit should
be allowed to stabilize for several minutes before meaningful measurements can be taken and the
conditioned room should be or near the temperature setpoint.
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