Calculating Charging Values For Liebert Mc Condenser Systems, Units Without Liebert Lee-Temp ™ Systems - Emerson Liebert CRV User Manual

6.7 Calculating Charging Values for Liebert MC Condenser Systems, Units without
Liebert Lee-Temp
The system must be fully piped and evacuated before it can be charged. See 6.6 Vacuum and
Refrigerant Charge.
Liebert MC condensers are charge-sensitive and require accurate calculation of the system charge to
avoid overcharging. To avoid overcharge, additional guidelines are recommended to ensure trouble
free operation.
• When charging system in an outdoor ambient below 50°F (10°C), recheck the subcooling against
Table 23 when the ambient is above 60°F (15.6°C)
• The indoor space should be maintained at 70 to 80°F (21 to 26.7°C) return air before final charge
adjustments are made.
• Charging unit at greater than 80°F (26.7°C) return air may result in the unit being overcharged.
• Charge by subcooling measurement at the indoor unit. See Table 23 for target subcooling
temperatures.
• Pressure and temperature measuring instruments should be capable of measuring to ±10 psig
(103.4kPa) and ± 2°F (1.1°C) for best subcooling measurement.
1. Check indoor nameplate for refrigerant type to be used. Unit control configurations differ
depending on refrigerant type.
2. Refrigerant charging requires unit operation. Refer to the indoor unit's user manual for details
regarding indoor unit operation and to the Liebert MC user manual, SL-19536, available at the
Liebert Web site (www.liebert.com), for the Liebert MC condenser operation.
3. Calculate the amount of charge for the system. Refer to the indoor unit user manual and to the
condenser and refrigerant line charge data in the Liebert MC user manual, SL-19536, available at
the Liebert Web site.
4. Accurately weigh in as much of the system charge as possible before starting the unit. Do not
exceed the calculated charge by more than 0.5 lb (.37kg).
NOTICE
Risk of improper refrigerant charging. Can cause equipment damage.
Refrigerant R-407C and R-410A are blended refrigerants and must be introduced and charged
from the cylinder only as a liquid.
When adding liquid refrigerant to an operating system, it may be necessary to add the
refrigerant through the compressor suction service valve. Care must be exercised to avoid
damage to the compressor. Emerson recommends connecting a sight glass between the
charging hose and the compressor suction service valve. This will permit adjustment of the
cylinder hand valve so that liquid can leave the cylinder while allowing vapor to enter the
compressor.
NOTICE
Risk of refrigerant overcharge. Can cause equipment damage.
Do not use the sight glass as an indicator when charging Liebert MC condenser systems.
5. Turn On the Liebert MC disconnect switch.
6. Turn on the indoor unit disconnect switch. Operate the unit for 30 minutes using the charging
function of the indoor unit control for each circuit of the system. The charging function is in the
diagnostic section of the Liebert iCOM
charging function operates the compressor(s) at full capacity and energizes the liquid line
solenoid valve(s). The reheat and humidifier are disabled. Manual operation of the indoor fans
from the diagnostic menu of the Liebert iCOM is required. A minimum 20psig (138kPa) must be
established and maintained for the compressor to operate. The charging function can be reset as
many times as required to complete unit charging.
7. Attach pressure and temperature instruments to the liquid line of the indoor unit. Measure the
initial subcooling and continue to add charge until recommended subcooling for the current
outdoor ambient temperature is reached. See Table 23. The outdoor ambient can be read from
the Liebert MC condenser control menu ID F02.
® ™
Liebert CRV
™
Systems
® control (see Liebert iCOM user manual, SL-18835). The
Refrigerant Connections for Air-Cooled Units
44