Johnson Controls YORK YVAM 0350, Operation & Maintenance Manual

Page: 135 / 162

4. Repeat the previous steps after the evaporator liquid has been removed by connecting a
liquid recovery connection to the compressor discharge line at the low point service valves.
Note that the compressor discharge line is the lowest point in the refrigerant circuit and
might contain condensed liquid refrigerant. Conducting liquid recovery at this location can
speed up the recovery process.
5. When all liquid refrigerant has been recovered, begin the vapor recovery process by
connecting to any of the chiller vapor service connections so that the refrigerant vapor can
be recovered and condensed into the refrigerant container. The chilled liquid pumps must
remain operational for this process because the vapor pressures can drop significantly below
the values that would cause water or brine to freeze. For water with R-134a at 32°F, that
pressure is 28 psig. See Table 95.
Checking and trimming the refrigerant charge
Important: The amount of chiller refrigerant charge must be verified to meet the specified
amount as found in the chiller factory order form (FOF). Reference this document or the unit
Sales Order screen on the chiller control panel to determine the amount of charge required
based on the chiller rating.
During operation, the refrigerant charge level is correct when the evaporator approach (STD),
subcooling, and compressor discharge superheat are at the design values for the condition. For
new sales, these design values are included as part of the FOF. For units where they are not seen
on the FOF, they can be provided upon request from the chillers sales engineer from the chiller
rating program. These depend on tube selection, chilled fluid type, operating head, and operating
condition. The following equations define these parameters. Condenser subcooling is calculated
and the condenser drain valve is controlled to the programmed setpoint by the chiller control logic.
Equations:
• Evaporator approach = (LCHLT) - (EST)
• Discharge superheat = (CDT) - (CST)
• Subcooling = (CST) - condensed refrigerant liquid temperature (from condenser outlet)
Definitions (based on OptiView panel operating data):
• EST = evaporator saturation temperature
• LCHLT = leaving evaporator liquid temperature
• CDT = compressor discharge temperature
• CST = condenser saturation temperature
You can view the parameters on the OptiView Control Center. The chiller must be at full load design
operating conditions so that the correct refrigerant charge level can be correctly determined when
operating. When proper condenser level is maintaining the design subcooling, the evaporator
approach and discharge superheat are a function of the amount of charge that is now maintained
in the evaporator. To lower evaporator STD and compressor discharge superheat, add the
refrigerant charge is added to the system. If additional details are needed, contact product
technical support (PTS) for guidance.
Checking the refrigerant charge during unit shutdown
Because YVAM uses a hybrid falling film technology, there is no reliable means to evaluate the
refrigerant charge when the chiller is not running.
Compressor and motor maintenance
• Check the mounting screws and piping joint nuts frequently to ensure tightness.
135 YVAM Control Center