Section 2 - System Operating Procedures; Pre-Starting; Start-Up; Chiller Operation - York YMC2 A Operation And Maintenance

Form 160.78-O1
Issue date: 05/19/2021

Pre-starting

Before starting the chiller, observe the OptiView
trol Center. Refer to the YMC
ter Operations Manual (Form 160.78-O2). Make sure
that the display reads "SYSTEM READY TO START".
Vent any air from the chiller waterboxes
before starting the water pumps. Failure
to do so will result in pass baffle damage.

Start-up

1. If the chilled water pump is manually operated,
start the pump. The Control Center will not al-
low the chiller to start unless chilled liquid flow
is established through the unit. If the chilled liq-
uid pump is wired to the Microcomputer Control
Center the pump will automatically start, there-
fore, this step is not necessary.
2. To start the chiller, press the RUN key on the
Home Screen on the display panel.
For display messages and information pertaining
to the operation of the OptiView™ Control Cen-
ter, refer to the YMC
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Operations Manual (Form 160.78-O2).
Any malfunctions which occur during
SHUTDOWN are also displayed.
The coolant temperature inside any JCI-supplied liq-
uid-cooled motor starter must be maintained above the
dewpoint temperature in the equipment room to prevent
condensing water vapor inside the starter cabinet. There-
fore, 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 evapo-
rative 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.
JOHNSON CONTROLS

Section 2 - System operating procedures

Con-
TM
OptiView Control Cen-
2 TM
OptiView Control Center
TM

Chiller operation

The chiller will vary capacity to maintain the leaving
chilled liquid temperature setpoint by a specific se-
quencing of optional hot gas bypass, pre-rotation vanes
or variable geometry diffuser, and compressor speed.
Throughout capacity control, the compressor speed is
maintained above the minimum required for the pre-
vailing head condition, to avoid surge. Otherwise, the
device maintaining capacity is controlled by a pro-
portional-integral-derivative control based on leaving
chiller liquid temperature. Pressure and motor current
overrides also apply as necessary to maintain operating
limits.

Condenser water temperature control

The YORK YMC chiller is designed to use less power
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by taking advantage of lower than design temperatures
that are naturally produced by cooling towers through-
out the operating year. Exact control of condenser wa-
ter such as a cooling tower bypass, is not necessary for
most installations. The minimum entering condenser
water temperature for other full and part-load condi-
tions is provided by the following equation:
where:
ECWT = entering condensing water temperature
LCHWT = leaving chilled water temperature
At initial startup, entering condensing water tempera-
ture 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 tow-
er fan cycling will normally provide adequate control
of the entering condenser water temperature on most
installations.

Operating logs

A permanent daily record of system operating condi-
tions (temperatures and pressures) recorded at regular
intervals throughout each 24-hour operating period
should be kept. Automatic data logging is possible by
connecting the optional printer and programming the
DATA LOGGER function. An optional status printer
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