Johnson Controls YORK YMC2 Installation guide

Form Number: 160.84-OM1 (521)
Supersedes: 160.84-OM1 (321)
Operation and Maintenance
Issue Date: 2021-05-10
YMC2 Mod B with OptiView™ Control
Center
Centrifugal Liquid Chiller with R-134a or R-513A Refrigerant

2YMC2 Mod B with OptiView™ Control Center

Contents
ContentsGeneral safety guidelines.............................................................................................................................. 7
Safety symbols..................................................................................................................................... 7
Changeability of this document......................................................................................................... 8
Associated literature........................................................................................................................... 8
Conditioned based maintenance...................................................................................................... 9
Nomenclature...................................................................................................................................... 9
System fundamentals.................................................................................................................................. 11
System components.......................................................................................................................... 11
Compressor.............................................................................................................................................. 11
Motor......................................................................................................................................................... 11
Heat exchangers...................................................................................................................................... 11
Evaporator................................................................................................................................................ 12
Condenser................................................................................................................................................. 12
Water boxes.............................................................................................................................................. 12
Refrigerant flow control.......................................................................................................................... 12
Variable speed drive................................................................................................................................ 12
Power panel.............................................................................................................................................. 12
Optional service isolation valves............................................................................................................ 12
Optional hot gas bypass......................................................................................................................... 13
OptiView™ control center........................................................................................................................ 13
System operation description.......................................................................................................... 15
Capacity control........................................................................................................................................ 16
Anti-surge minimum frequency............................................................................................................. 17
Smart freeze............................................................................................................................................. 17
Surge protection...................................................................................................................................... 17
Head pressure control............................................................................................................................. 17
System operating procedures.................................................................................................................... 19
Pre-starting......................................................................................................................................... 19
Condenser water temperature control........................................................................................... 19
Start-up............................................................................................................................................... 19
Chiller operation................................................................................................................................ 20
Chilled liquid control settings.......................................................................................................... 21
Operator setpoints quick reference................................................................................................ 22
Stopping the system......................................................................................................................... 23
Safety stop.......................................................................................................................................... 23
Operating logs................................................................................................................................... 23
Fault shutdowns................................................................................................................................ 24
Prolonged shutdown......................................................................................................................... 24
Restart after prolonged shutdown.................................................................................................. 25
OptiView control center functions and navigation.................................................................................. 28
Interface conventions....................................................................................................................... 28
YMC2 Mod B with OptiView™ Control Center 3

Display only........................................................................................................................................ 28
Programmable................................................................................................................................... 28
Navigation.......................................................................................................................................... 29
Languages.......................................................................................................................................... 30
Analog input ranges.......................................................................................................................... 30
Home screen...................................................................................................................................... 32
System screen.................................................................................................................................... 35
Evaporator screen............................................................................................................................. 37
Condenser screen.............................................................................................................................. 40
Heat pump screen............................................................................................................................. 42
Compressor screen........................................................................................................................... 47
Magnetic bearing controller screen................................................................................................ 49
Magnetic bearing controller details screen................................................................................... 51
Surge screen...................................................................................................................................... 54
Variable geometry diffuser screen.................................................................................................. 56
Power panel screen........................................................................................................................... 58
Capacity control screen.................................................................................................................... 60
Variable speed drive screen............................................................................................................. 63
Variable speed drive (VSD) details screen...................................................................................... 66
Motor details screen......................................................................................................................... 68
Setpoints screen................................................................................................................................ 70
Setup screen...................................................................................................................................... 73
Schedule screen................................................................................................................................. 77
User screen........................................................................................................................................ 79
Comms screen................................................................................................................................... 80
Printer screen..................................................................................................................................... 82
Sales order screen............................................................................................................................. 84
Operations screen............................................................................................................................. 86
History screen.................................................................................................................................... 87
History details screen....................................................................................................................... 89
Custom screen................................................................................................................................... 90
Custom setup screen........................................................................................................................ 91
Trend screen...................................................................................................................................... 93
Trend setup screen........................................................................................................................... 95
Advanced trend setup screen.......................................................................................................... 98
Common slots screen..................................................................................................................... 101
Master slot numbers list for use with trend feature................................................................... 102
Display messages............................................................................................................................ 106
VSD operation............................................................................................................................................. 140
OptiSpeed compressor drive overview......................................................................................... 140
OptiSpeed compressor drive features.......................................................................................... 140
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OptiSpeed compressor drive details (0490 and 0774 amp drives).................................................. 141
Smart sensor system............................................................................................................................. 142
OptiSpeed compressor drive details (0490A, 0612A, 0730A, and 1278A amp drives).................... 143
OptiSpeed compressor drive and chiller operation (0490 and 0774 amp models)................. 154
OptiSpeed compressor drive and chiller operation (0490A, 0612A, 0730A, and
1278A amp models)............................................................................................................... 155
Maintenance............................................................................................................................................... 156
Preventative maintenance............................................................................................................. 156
Renewal parts.................................................................................................................................. 157
Operating inspections.................................................................................................................... 157
Checking system for leaks.............................................................................................................. 158
Conduct pressure test.................................................................................................................... 158
System evacuation.......................................................................................................................... 160
Vacuum dehydration....................................................................................................................... 160
Conduct pressure test.................................................................................................................... 163
Refrigerant charging....................................................................................................................... 163
Checking the refrigerant charge................................................................................................... 163
Handling refrigerant for dismantling and repairs...................................................................... 164
Compressor and motor.................................................................................................................. 164
Condensers and evaporators........................................................................................................ 165
Chemical water treatment.................................................................................................................... 165
Cleaning evaporator and condenser tubes........................................................................................ 166
Tube fouling............................................................................................................................................ 166
Tube cleaning procedures.................................................................................................................... 166
Acid cleaning of tubes........................................................................................................................... 166
Testing for evaporator and condenser tube leaks............................................................................ 167
Electrical controls............................................................................................................................ 168
Automatic battery health test – during shutdown...................................................................... 168
Printing........................................................................................................................................................ 170
Printing overview............................................................................................................................. 170
Acceptable printers......................................................................................................................... 170
OKI Data.................................................................................................................................................. 171
Brecknell................................................................................................................................................. 172
Control center setup....................................................................................................................... 173
Downloading system prints to a laptop....................................................................................... 174
Unit conversion.......................................................................................................................................... 184
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6YMC2 Mod B with OptiView™ Control Center

General safety guidelines
Important: Read before proceeding.
This equipment is a relatively complicated apparatus. During rigging, installation, operation,
maintenance, or service, individuals may be exposed to certain components or conditions including,
but not limited to: heavy objects, refrigerants, materials under pressure, rotating components, and
both high and low voltage. Each of these items has the potential, if misused or handled improperly,
to cause bodily injury or death. It is the obligation and responsibility of rigging, installation, and
operating/service personnel to identify and recognize these inherent hazards, protect themselves,
and proceed safely in completing their tasks. Failure to comply with any of these requirements could
result in serious damage to the equipment and the property in which it is situated, as well as severe
personal injury or death to themselves and people at the site.
This document is intended for use by owner-authorized rigging, installation, and operating/service
personnel. It is expected that these individuals possess independent training that will enable them
to perform their assigned tasks properly and safely. It is essential that, prior to performing any
task on this equipment, this individual shall have read and understood the on-product labels, this
document and any referenced materials. This individual shall also be familiar with and comply
with all applicable industry and governmental standards and regulations pertaining to the task in
question.
Safety symbols
The following symbols are used in this document to alert the reader to specific situations:
DANGER
Indicates a possible hazardous situation which will result in death or serious injury if proper care is not
taken.
WARNING
Indicates a potentially hazardous situation which will result in possible injuries or damage to equipment
if proper care is not taken.
CAUTION
Identifies a hazard which could lead to damage to the machine, damage to other equipment and/or
environmental pollution if proper care is not taken or instructions and are not followed.
Note: Highlights additional information useful to the technician in completing the work being
performed properly.
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YMC2 Mod B with OptiView™ Control Center

WARNING
External wiring, unless specified as an optional connection in the manufacturer’s product line, is not
to be connected inside the control cabinet. Devices such as relays, switches, transducers and controls
and any external wiring must not be installed inside the micro panel. All wiring must be in accordance
with Johnson Controls’ published specifications and must be performed only by a qualified electrician.
Johnson Controls will NOT be responsible for damage/problems resulting from improper connections
to the controls or application of improper control signals. Failure to follow this warning will void the
manufacturer’s warranty and cause serious damage to property or personal injury.
Changeability of this document
In complying with Johnson Controls’ policy for continuous product improvement, the information
contained in this document is subject to change without notice. Johnson Controls makes no
commitment to update or provide current information automatically to the manual owner. Updated
manuals, if applicable, can be obtained by contacting the nearest Johnson Controls Service office or
accessing the Johnson Controls Knowledge Exchange website at https://docs.johnsoncontrols.com/
chillers/.
Operating/service personnel maintain responsibility for the applicability of these documents to the
equipment. If there is any question regarding the applicability of these documents, the technician
should verify whether the equipment has been modified and if current literature is available from
the owner of the equipment prior to performing any work on the chiller.
Revision notes
Revisions made to this document are indicated in the following table. These revisions are to
technical information,and any other changes in spelling, grammar, or formatting are not included.
Table 1: Revision notes
Affected pages Description
156 Updated maintenance requirements table
157 Updated operating inspections
Associated literature
Manual description Form number
Installation and Reassembly 160.84-N1
Unit Installation Checklist and Request for Startup 160.84-CL1
Unit Startup Checklist 160.84-CL2
Field Connections Diagram 160.84-PW1
Field Control, Wiring and MBC Diagrams 160.84-PW2
Field Connections with MV Electro-Mech Starters 160.84-PW3
Electro-Mechanical Starter 160.84-PW4
Unit Replacement Parts - YMC 2 Mod B 160.84-RP1
Unit Replacement Parts - YMC 2 Mod B with M6 Compressor 160.84-RP2
VSD Replacement Parts 160.84-RP3
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Manual description Form number
Centrifugal Chiller Long Term Storage 50.20-NM5
All Products - Replacement Parts Electrical Connectors 50.20-RP1
All Products - Replacement Parts Fittings 50.20-RP2
Conditioned based maintenance
Traditional chiller maintenance is based upon assumed and generalized conditions. In lieu of
the traditional maintenance program, a Johnson Controls YORK Conditioned Based Maintenance
(CBM) program can be substituted. This CBM service plan is built around the specific needs for
the chiller, operating conditions, and annualized impact realized by the chiller. Your local Johnson
Controls Branch can propose a customized Planned Service Agreement that leverages real time
and historical data, delivering performance reporting, corrective actions required and data enabled
guidance for optimal operation and life cycle assurance. The program will include fault detection
diagnostics, operation code statistics, performance based algorithms and advance rules based
rationale delivered by the Johnson Controls Connected Equipment Portal.
Nomenclature
Figure 1: System nomenclature
Figure 2: Compressor nomenclature
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YMC2 Mod B with OptiView™ Control Center

Figure 3: Vessel nomenclature
Figure 4: Variable speed drive nomenclature
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System fundamentals
System components
The YORK Model YMC2 Centrifugal Liquid Chiller is completely factory-packaged including
evaporator, condenser, compressor, motor, variable speed drive, battery power panel, OptiView™
Control Center, and all interconnecting unit piping and wiring (see Figure 5).
Figure 5: YMC2 chiller components
Compressor
The compressor is a single-stage centrifugal type powered by a hermetic electric motor, on a
common shaft with a cast aluminum, fully shrouded impeller. The compressor has fixed inlet vanes
and variable geometry diffuser.
Motor
The compressor motor is a hermetic permanent magnet high speed design with magnetic
bearings. The compressor impeller is overhung from the end of the motor shaft and has no
bearings of its own.
The motor includes angular contact ball bearings only engaged with the rotor shaft during
shutdown after rotation is stopped or during shutdown due to loss of power to the magnetic
bearings.
The bearing control center maintains correct shaft position in the magnetic bearings.
Heat exchangers
Evaporator and condenser shells are fabricated from rolled carbon steel plates with fusion welded
seams. Heat exchanger tubes are internally enhanced type.
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YMC2 Mod B with OptiView™ Control Center

Evaporator
The evaporator is a shell and tube, hybrid falling film, and flooded type heat exchanger. A
distributor trough provides uniform distribution of refrigerant over tubes in the falling film section.
Residual refrigerant floods the tubes in the lower section. Suction baffles are located above the
tube bundle to prevent liquid refrigerant carryover into the compressor. A 2 in. liquid level sight
glass is located on the side of the shell. The evaporator shell contains dual refrigerant relief valves
unless condenser isolation is installed.
Condenser
The condenser is a shell and tube type, with a discharge gas baffle to prevent direct high
velocity impingement on the tubes. A separate subcooler is located in the condenser to enhance
performance. Dual refrigerant relief valves are located on condenser shells and optional refrigerant
isolation valves are available.
Water boxes
The removable compact water boxes are fabricated of steel. The design working pressure is 150
PSIG (1034 kPa) and the boxes are tested at 225 PSIG (1551 kPa). Integral steel water baffles
provide the required pass arrangements. Stub-out water nozzle connections with Victaulic grooves
are welded to the water boxes. These nozzle connections are suitable for Victaulic couplings,
welding or flanges, and are capped for shipment. Plugged 3/4 in. drain and vent connections are
provided in each water box. Optional marine waterboxes and higher pressure ratings are available.
Refrigerant flow control
Refrigerant flow to the evaporator is controlled by the liquid level control valve.
A level sensor senses the refrigerant level in the condenser and outputs an analog voltage to the
control panel that represents this level (0% = empty; 100% = full). Under program control, the
control panel modulates the liquid level control valve to control the condenser refrigerant level
to a programmed setpoint. Other setpoints affect the control sensitivity and response. Only a
qualified service technician may modify these settings. The level setpoint must be entered at chiller
commissioning by a qualified service technician.
While the chiller is shut down, the level control valve will be pre positioned to anticipate run. When
the chiller is started, if actual level is less than the level setpoint, a linearly increasing ramp is
applied to the level setpoint. This ramp causes the setpoint to go from the initial refrigerant level
to the programmed setpoint over a programmable period of time. If the actual level is greater than
the setpoint upon run, it immediately begins to control to the programmed setpoint.
While the chiller is running, the refrigerant level is normally controlled to the level setpoint.
Variable speed drive
A Variable Speed Drive will be factory packaged with the chiller. It is designed to vary the
compressor motor speed by controlling the frequency and voltage of the electrical power to the
motor. The control logic automatically adjusts motor speed as required to suit lift and capacity
requirements.
Power panel
The power panel includes the uninterrupted power supply and power storage battery. These feed
essential loads while the chiller shuts down upon loss of main chiller power.
Optional service isolation valves
If your chiller is equipped with optional service isolation valves on the discharge and liquid line,
these valves must remain open during operation. These valves are used for isolating the refrigerant
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charge in either the evaporator or condenser to allow service access to the system. A refrigerant
pump-out unit will be required to isolate the refrigerant.
CAUTION
Isolation of the refrigerant in this system must be performed by a qualified service technician.
Optional hot gas bypass
Hot gas bypass is optional and is used to provide greater turndown than otherwise available for
load and head conditions. The OptiView Control Center will automatically modulate the hot gas
valve open and closed as required. Adjustment of the hot gas control valve must only be performed
by a qualified service technician.
OptiView™ control center
The YORK OptiView™ control center LCD Graphic Display and keypad is the interface for starting,
stopping, configuring, monitoring, and commanding the chiller controls. The control center is a
microprocessor based system for centrifugal chillers. It controls the LCHLT and maintains safe
operation. It is factory-mounted, wired and tested.
The graphic display allows the presentation of operating parameters in logical groups on screens
and can trend data to present a graphical representation of present or historical operation of the
chiller. The locations of various chiller parameters are clearly and intuitively marked. Instructions
for specific operations are provided on many of the screens. The screens and navigation are shown
in the OptiView Control Center Functions and Navigation section of this manual.
Eight buttons are available on the right side of the panel, and are primarily used for navigation
between the system screens. At the base of the display are 5 additional buttons. The button
functions are redefined based on the currently displayed screen. The area to the right of the keypad
is used for data entry with a standard numeric keypad provided for entry of system setpoints and
limits.
Figure 6: OptiView Control Center
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YMC2 Mod B with OptiView™ Control Center

Table 2: OptiView control center buttons
Button Description
The Decimal button provides accurate entry of setpoint
values.
A ± button has also been provided to allow entry of negative
values and AM/PM selection during time entry.
In order to accept changes made to the chiller setpoints, the
Check button is provided as a universal ‘Enter’ key or ‘Accept’’
symbol.
In order to reject entry of a setpoint or dismiss an entry form,
the ‘X’ button is provided as a universal ‘Cancel’ symbol.
Cursor Arrow buttons are provided to allow movement
on screens which contain a large amount of entry data. In
addition, these buttons can be used to scroll through history
and event logs.
The graphic display also allows numerical information to be represented in both English
(temperatures in °F and pressures in psig) and Metric (temperatures in °C and pressures in kPa)
mode. It also has the ability to display many languages.
The control center continually monitors the system operation and records the cause of any
shutdowns (Safety, Cycling, or Normal). This information is recorded in memory and is preserved
even through a power failure condition. The user may recall it for viewing at any time. During
operation, the user is continually advised of the operating conditions by various status and warning
messages. In addition, it may be configured to notify the user of certain conditions via alarms. A
complete listing of shutdown, status, and warning messages is attached in Display messages.
The control center includes capabilities for remote control and communications. Common
networking protocol through the Building Automation System (BAS) allows increased remote
control of the chiller, as well as 24-hour performance monitoring via a remote site. An optional
circuit board called the SC-EQUIP provides Johnson Controls and YORK mechanical equipment such
as the YMC2 chiller with building automation system (BAS) networking connectivity.
The chiller also maintains the standard digital remote capabilities as well. Both of these remote
control capabilities allow for the following standard Energy Management System (EMS) interfaces.
The actual connection details are in the Field Connections section of the Wiring Diagram (Form
160.84-PW1 and PW3):
• Remote Start
• Remote Stop
• Remote Leaving Chilled Liquid Temperature Setpoint adjustment: BAS coms, Analog signal,
(0-10 VDC, 2-10 VDC, 0-20 mA or 4-20 mA) or pulse width modulation (PWM)
• Remote Current Limit Setpoint adjustment: BAS coms, Analog signal, (0-10 VDC, 2-10 VDC, 0-2
0mA or 4-2 0mA) or pulse width modulation
• Remote “Ready to Start” Contacts
• Safety Shutdown Contacts
• Cycling Shutdown Contacts
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The OptiView panel can be used to control the customer chilled and condenser liquid flow. A set
of contacts exists to initiate flow for each shell. Details are in the Field Connections section of the
Wiring Diagram (Form 160.84-PW2 and PW4). The chilled water pump contacts close immediately
upon execution of a chiller start command. They open coincident with the receipt of a stop
command or a fault other than those below:
1. LEAVING CHILLED LIQUID - LOW TEMPERATURE cycling shutdown.
2. MULTIUNIT CYCLING - CONTACTS OPEN or SYSTEM CYCLING - CONTACTS OPEN (Only if
Chilled Liquid Pump Operation is set to ENHANCED)
3. LEAVING CHILLED LIQUID FLOW SWITCH OPEN cycling shutdown
The Condenser Pump contacts close immediately upon execution of a chiller start command.
They open coincident with receipt of a chiller stop command or fault other than CONDENSER-FLOW
SWITCH OPEN cycling shutdown.
If the chiller is Stopped and the Condenser Pump contacts are open (flow off), the contacts close
when Saturated Condenser Temperature is less than 35.0°F. This helps mitigate condenser freeze
due to plant issues in brine applications.
If the contacts are closed only due to the Saturated Condenser Temp, they are opened when
Saturated Condenser Temperature returns above 40.0°F. If the existing logic calls for them to be
closed, they remain closed.
Some screens, displayed values, programmable setpoints and manual controls exist for service
technician use only. They are only displayed when logged in at SERVICE access level or higher. The
setpoints and parameters displayed on these screens are explained in detail in YORK YMC2 Service
Manual (Form 160.84-M2). These parameters affect chiller operation and should never be modified
by anyone other than a qualified service technician. The advanced diagnostics and troubleshooting
information for service technicians are included in YORK YMC2 Service Manual (Form 160.84-M2). Also
included in the Service manual are detailed descriptions of chiller features, such as capacity control,
refrigerant level control, variable geometry diffuser, and magnetic bearing controller.
The chiller operating program resides in the OptiView Control Center microboard. Software
versions (C.OPT.18.xx.yzz) are alpha-numeric codes that represent the application, language
package and revision levels as below. Each time the controls portion or language section is revised,
the respective revision level increments.
•C: commercial Chiller
•OPT: OptiView
•18: YMC2 Mod B Chiller
•xx: Controls Revision level (00, 01, etc)
•y: Language Package (0=English only, 1=NEMA, 2=CE, 3=NEMA/CE )
•zz: Language Package Revision level (00, 01, etc)
Software upgrades should only be performed by a service technician.
System operation description
In operation, a liquid to be chilled (water or brine) flows through the evaporator tubes, where its
heat is transferred to low pressure liquid refrigerant sprayed over and pooled outside the tubes,
boiling the refrigerant. The chilled liquid is then piped to air conditioning or process terminal units,
absorbing heat. The warmed liquid is then returned to the chiller to complete the chilled liquid
circuit cycle.
The refrigerant vapor, which is produced by the boiling action in the evaporator, is drawn into the
suction of the compressor where the rotating impeller increases its pressure and temperature and
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YMC2 Mod B with OptiView™ Control Center

discharges it into the condenser. Cooling water (or other fluid) flowing through the condenser
tubes absorbs heat from the refrigerant vapor, causing it to condense. The cooling water is
supplied to the chiller from an external source, usually a cooling tower. The condensed refrigerant
drains from the condenser into the subcooler section. There it is cooled by the entering condenser
water and exits to into the liquid return line. The level control valve meters the flow of liquid
refrigerant to the evaporator to complete the refrigerant circuit. The level control valve continually
adjusts position as load changes to meet the changed mass flow rate of refrigerant required to
keep the system balanced. It does this by maintaining a constant level in the condenser, enough to
maintain a liquid seal to the outlet.
Capacity control
The major components of a chiller are selected to handle the required refrigerant flow at full load
design conditions. However, most systems will be called upon to deliver full load capacity for only
a relatively small part of the time the unit is in operation. A means exists to modulate capacity for
other loads.
The speed at which the compressor rotates establishes the pressure differential that the chiller can
operate against. This is referred to as ‘lift’. Speed must always be maintained above the minimum
necessary to create the lift required for the pressure difference between the condenser and
evaporator, regardless of load. Below that speed, gas surge occurs. That pressure difference is a
function of the LCHLT and the leaving condenser liquid temperature and the heat transfer between
those liquids and the refrigerant.
Reduced speed also reduces the available capacity of the chiller, when speed reduction is possible.
If speed is reduced, the chiller power use is reduced. Therefore, at reduced capacity requirements
where condenser pressure is also reduced, the motor speed is reduced as much as possible
while maintaining chilled liquid temperature and sufficient lift. When the speed cannot be further
reduced due to lift required for the specified leaving chilled water temperature setting and
available cooling to the condenser and capacity must be further reduced, a mechanism called
Variable Geometry Diffuser (VGD) at the exit of the impeller is used to reduce refrigerant gas flow.
The VGD not only controls capacity, but serves to mitigate “stall”. Stall is an effect caused by slow
refrigerant gas passing through the compressor at reduced flow rates needed for low capacity
operation.
A final optional means to reduce capacity called Hot Gas Bypass (HGBP) is available regardless of
compressor model. When selected for an application, HGBP is used to re-circulate some refrigerant
through the compressor without using it for cooling the chilled liquid. Although this does not
reduce power consumption, it greatly reduces the capacity of the chiller for maximum turndown.
The YMC2 uses these mechanisms in a controlled order to maintain best efficiency.
The YMC2 Chiller controls capacity by adjusting the compressor VGD position, the compressor
motor Variable Speed Drive (VSD), and optional Hot Gas Bypass valve (HGBP) position (if equipped)
in a specific sequence depending on whether loading or unloading is required to keep Leaving
Chilled Liquid Temperature at setpoint. Motor speed is additionally and simultaneously adjusted as
necessary to maintain the minimum compressor lift required to prevent surge. The sequence for
operation of the control devices is as follows to achieve the best chiller efficiency:
• Conditions require capacity increase: HGBP (if present) is driven toward closed. Then when
the HGBP is full closed, VGD is driven toward open. Then when the VGD is full open, VSD
speed is increased.
• Conditions require capacity decrease: VSD speed is decreased. Then when VSD speed is at
the minimum limit to avoid surge for the lift, the VGD is driven toward closed. Then when the
VGD reaches closed, the HGBP (if present) is driven toward open.
Also, High Condenser Pressure, Low Evaporator Pressure, High Motor Current, and High Input
Current limits and overrides limit or reduce the output to the appropriate devices (HGBP, VGD, or
VSD) to mitigate the condition to keep the chiller online. As any of these physical thresholds are
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16

approached, the control will proportionally limit the amount of capacity increase permitted and if
exceeded will issue unloading into the capacity control command.
Anti-surge minimum frequency
In order to maintain sufficient compressor lift to overcome condenser pressure and prevent surge
throughout operation, the control maintains and continuously updates a minimum limit for VSD
speed. This limit is the Active Anti-Surge Minimum Frequency. It is calculated and applied to the
speed each cycle of the capacity control routine.
Smart freeze
The Smart Freeze feature prevents nuisance chiller shutdowns due to brief periods of chilled liquid
flow fluctuations or other brief operating conditions that would normally cause Low Evaporator
Pressure Safety shutdowns. With this feature enabled and activated, the chiller is permitted to
ride through these temporary conditions. Also, this feature allows the Leaving Chilled Liquid
Temperature Setpoint to be set as low as 36.0ºF (2.2ºC). Smart Freeze protection can be enabled or
disabled at the Keypad, by a service technician. It cannot be used in Brine cooling mode.
Smart Freeze protection uses the Evaporator Refrigerant Temperature as one of the variables to
determine when freezing is imminent. The basis of this feature is that the chilled liquid contains an
amount of heat, which cannot be eliminated immediately. Therefore, it requires a certain amount of
time for the liquid to change to a solid. During this period of time, those parameters that determine
when solidification will occur are evaluated and the shutdown is based on accumulated time below
the freeze temperature.
Surge protection
The surge protection feature detects surge events. It provides a running count of the surges
detected over the lifetime of the chiller. It allows the user to define how many surges are excessive
and how the control will react to an excess surge condition. When excessive surging is detected,
this feature can shutdown the chiller.
Surge events are detected by monitoring the relationship between the Condenser pressure
and Evaporator pressure while the chiller is running. An excess surge condition is detected by
comparing the number of surge events that occur in a selectable time period to a selectable
threshold.
If the number of surge events (Surge Window Count) detected in the time period programmed as
the COUNT WINDOW setpoint (1 to 5 minutes; default 5) exceed the threshold programmed as the
COUNT LIMIT setpoint (4 to 20; default 4) an excess surge condition has been detected.
Unless the SHUTDOWN features have been enabled, as explained below, the chiller will continue to
run under the same conditions displaying WARNING – EXCESS SURGE DETECTED. This message
will be displayed until manually reset with the Warning Reset key in Operator access level. If the
SHUTDOWN setpoint is Enabled, when an excess surge condition has been detected a safety
shutdown will be performed and SURGE PROTECTION - EXCESS SURGE is displayed.
Head pressure control
The Head Pressure Control feature enables chiller control of a field-mounted facility condenser
water temperature control means, if one is necessary for prolonged cold water startup as described
in OptiView control center functions and navigation. YMC2 chillers are capable of operation
within a wide range of condenser water temperatures. However, a low minimum condenser
water temperature, as specified in the YMC2 Engineering Guide (Form 160.84-EG1), is required to
maintain sufficient pressure differential (head) between the condenser and evaporator for correct
refrigerant management in the chiller. The head pressure control function provides an analog
output control signal from the OptiView Control Center that responds to the programmed Head
Pressure (condenser pressure minus evaporator pressure) Setpoint. The 0-10 VDC or 4-20 mA
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YMC2 Mod B with OptiView™ Control Center

output is configurable from the Head Pressure Control screen when the feature is Enabled. Output
wiring is described in the Field Connections section of the Wiring Diagram (Form 160.84-PW2 and
PW4):
Figure 7: Refrigerant flow-through chiller
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18

System operating procedures
Pre-starting
Before starting the chiller, make sure the display reads SYSTEM READY TO START.
The panel can only boot up when line power is available to the VSD transformers and the UPS
battery in the power panel is present and connected with its disconnect closed.
CAUTION
After periods of waterside maintenance or prolonged shutdown, vent any air from the chiller water
boxes prior to starting the water pumps. Failure to do so can result in pass baffle damage.
Condenser water temperature control
The YORK YMC2 chiller is designed to use less power by taking advantage of lower than design
temperatures that are naturally produced by cooling towers throughout the operating year. Exact
control of condenser water such as a cooling tower bypass, is not necessary for most installations.
The minimum entering condenser water temperature for other full and part-load conditions is
provided by the following equation:
where:
ECWT = entering condensing water temperature LCHWT = leaving chilled water
temperature
At initial startup, entering condensing water temperature may be as much as 30°F (16.66°C) colder
than the standby chilled water temperature.
Min ECWT = LCHWT -30°F (16.66°C)
At start-up, the entering condenser water temperature may be as much as 30°F (16.66°C) colder
than the standby return chilled water temperature. Cooling tower fan cycling will normally provide
adequate control of the entering condenser water temperature on most installations.
Start-up
If the chilled water and/or condenser water pumps are manually operated, start the pump. The
Control Center will not allow the chiller to start unless chilled liquid flow is established through the
unit. If the liquid pumps are wired to the Microcomputer Control Center pump run contacts, the
pump will automatically start, therefore, this step is not necessary.
Note: The coolant temperature inside any JCI-supplied liquid-cooled motor starter must be
maintained above the dewpoint temperature in the equipment room to prevent condensing
water vapor inside the starter cabinet. Therefore, an additional temperature-controlled throttle
valve is needed in the flow path for the starter heat exchanger to regulate cooling above the
equipment room dewpoint for applications using cooling sources other than evaporative air-
exchange methods, such as wells, bodies of water, and chilled water. The temperature control
valve should be the type to open on increasing drive coolant temperature, fail-closed, and set
for a temperature above dewpoint. It can be requested as factory-supplied on a chiller order
by special quotation.
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YMC2 Mod B with OptiView™ Control Center

The Start/Stop control depends whether the chiller Control Source is set to Local or one of the
Remote types from the chiller Setup - Operations screen. Start is operated:
• only the keypad when the chiller is set to local mode,
• remotely through digital inputs in digital or analog remote mode but local keypad start must
be pressed initially to enable the run permissive, or
• by the SC-EQUIP in BAS (ISN) remote mode but local keypad start must be pressed initially to
enable the run permissive.
To start the chiller press the START key on the Home Screen on the display panel. In LOCAL
control source, the chiller then starts. In remote ISN, ANALOG, DIGITAL, or MODEM a remote start
command must also be provided to the correct input connection.
When the control is changed to local mode from any other source, it will remain in RUN if already
running or remain in STOP if already stopped. A hardware Safety Stop button is also located on the
side of the panel.
The chiller will start if the following conditions are met:
• Leaving Chilled Liquid Temperature is above the setpoint
• Chilled liquid flow is established
• Condenser liquid flow is established
• No uncleared faults or start inhibits exist
Chiller operation
Upon start request, the following occur in sequence:
1. Chiller's system pump run contacts close
2. VSD pre-charges (~12 seconds)
3. VSD pre-regulates (~3 seconds)
4. Motor runs
The chiller will vary capacity to maintain the leaving chilled liquid temperature setpoint by a specific
sequencing of optional hot gas bypass, variable geometry diffuser, and compressor speed.
Throughout capacity control, the compressor speed is maintained above the minimum required
for the prevailing head condition, to avoid surge. Otherwise, the device maintaining capacity is
controlled by a proportional-integral-derivative control based on leaving chiller liquid temperature.
Pressure and motor current overrides also apply as necessary to maintain operating limits.
The Input Current limit threshold value is determined from several settings, depending on the
chiller control source selected according to the Table 3.
Table 3: Input current limit threshold
Control source Active input current limit threshold
Local Lowest of: Local Input Current Limit Setpoint (% Input Job FLA) Pulldown Input
Current Limit (when active)
ISN Remote Input Current Limit Setpoint (comms)
Analog Remote Lowest of: Local Input Current Limit Setpoint (% Input Job FLA) Analog Remote
Input Current Limit Setpoint Pulldown Input Current Limit (when active)
Digital Remote Lowest of: Local Input Current Limit Setpoint (% Input Job FLA) Digital Remote
Input Current Limit Setpoint Pulldown Input Current Limit (when active)
YMC2 Mod B with OptiView™ Control Center
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