Quantech QWC4, Installation Operation & Maintenance, Page: 137 / 156

QUANTECH
137
SECTION 7 - MAINTENANCE
FORM QWC4-NM1 (221)
ISSUE DATE: 02/28/2021
7
Determining Correct Refrigerant Charge Level
The refrigerant charge level is correct when the con-
denser level is about 1 in. above the subcooler, and
the measured Evaporator Approach and Discharge
Refrigerant Gas Superheat are at the design values
for the condition. The equations (below) define these
parameters.
The chiller must be at design operating
conditions and full load operation before
the correct refrigerant charge level can be
properly determined.
Equations:
• Evaporator Approach = (SET) - (LELT)
• Discharge Superheat = (CDGT) - (SCT)
Definitions Of Temperatures:
• SET = Saturated Evaporator Temperature
• LELT = Leaving Evaporator Liquid Temperature
• CDGT = Compressor Discharge Gas Temperature
• SCT = Saturated Condensing Temperature
The parameters can be obtained from the control
center.
Liquid refrigerant will be visible in the evaporator
sight glass, but the refrigerant level cannot be properly
determined by viewing the liquid refrigerant level in
the evaporator sight glass.
Form 1 QWC4 chillers are charged with the correct
amount of refrigerant. Under some operating condi-
tions, the chiller may appear to be overcharged or un-
dercharged with refrigerant. Consult with a Quantech
Field Service Office before removing or adding refrig-
erant.
REFRIGERANT CHARGING
If necessary, add refrigerant charge to the QWC4 chill-
er until the evaporator approach and discharge super-
heat values are within design values.
A charging valve is located in the liquid line below the
evaporator. The charging connection is a 3/4 in. male
flare. Purge air and non-condensables from the charg-
ing hose. Add only new refrigerant, or refrigerant that
has been tested and certified to meet American Refrig-
eration Institute Standard (ARI-700).
HANDLING REFRIGERANT FOR
DISMANTLING AND REPAIRS
If it becomes necessary to open any part of the refriger-
ant system for repairs, remove the charge first.
To avoid the possibility of freezing liquid within the
evaporator tubes when charging an evacuated system,
only refrigerant vapor from the top of the drum or cyl-
inder must be admitted to the system until the system
pressure is raised above the point corresponding to the
freezing point of the evaporator liquid. For water, the
pressure corresponding to the freezing point is 29 psig
(20 kPa) for R-134a (at sea level).
While charging, take every precaution to prevent air
from entering the system. Make up a suitable charg-
ing connection from new copper tubing or approved
refrigerant hose to fit between the system charging
valve and the fitting on the charging cylinder. This con-
nection should be as short as possible but long enough
to permit sufficient flexibility for changing cylinders.
The charging connection should be purged each time
a full container of refrigerant is connected and chang-
ing containers should be done as quickly as possible to
minimize the loss of refrigerant.
Checking the Motor Windings
Make sure the motor power leads are marked and dis-
connect them from the output terminals in the VSD.
• Use a resistance meter to measure the winding re-
sistance phase-to-phase as shown in Figure 67 on
page 138
. The nominal values are listed below,
but the preventive maintenance program should
trend the values for gross changes.
• 400 VAC application: 24 mΩ for T1-T2, T2-
T3, T3-T1.
• 460 VAC application: 40 mΩ for T1-T2, T2-
T3, T3-T1.