York YR Manual page 15

FORM 160.81-O1 (1020)
ISSUE DATE 10/05/2020
A liquid level sensor, located in the condenser, detects
the refrigerant level. The refrigerant level in the con-
denser is expressed as 0% (minimum) to 100% (maxi-
mum). While the chiller is shutdown, an open signal is
applied to the actuator, driving the Orifice to the fully
open position. When the chiller is started, a close sig-
nal is applied to the Orifice actuator for the duration of
the "Start Sequence Initiated" period. This positions it
to approximately the 75% closed position prior to start-
ing the compressor motor, which occurs at the end of
the "Start Sequence Initiated" period.
To allow for actuator timing variances and assure the
valve is positioned at the 75% closed position, the du-
ration of the "Start Sequence Initiated" period is pro
grammable over the range of 30 to 300 seconds with
the Valve Preset Time setpoint. This position is held
for the first 3 minutes of "System Run". After the first
3 minutes, if the actual level is greater than or less than
the setpoint, a linearly increasing or decreasing ramp is
applied to the Level setpoint. This ramp causes the set-
point to increase or decrease (as appropriate) from the
actual position to the programmed setpoint over a de-
fined period. With software version C.OPT.05.08.303
(and earlier), this period is 15 minutes. With software
version C.OPT.05.09.303 (and later), this period is pro-
grammable over a range of 3 to 15 minutes using the
RAMP-UP TIME setpoint.
During the remainder of chiller run, the actuator is
modulated to maintain the programmed Level setpoint
(20 to 80%). This setpoint and others that affect this
operation are programmed by the Service Technician
on the REFRIGERANT LEVEL CONTROL screen. In
software version C.OPT.05.09.303 (and later), an off-
set is added to the Level Control setpoint during Low
Discharge Superheat events. This offset is displayed
on the REFRIGERANT LEVEL CONTROL screen as
REFRIGERANT LEVEL SETPOINT OFFSET. This
offset is calculated, over the range of 0% to (80% mi-
nus programmed Level setpoint), as follows:
• When the chiller is not running, the offset is 0%.
• The offset remains at 0% during the level control
valve preset and during the ramp after chiller start.
• When Discharge Superheat is less than 14ºF and
the Evaporator Pressure is more than 28.0 PSIG,
add 1% to the offset every 15 seconds, not to ex-
ceed the maximum offset.
• When Discharge Superheat more than 20ºF sub-
tract 1% from the offset every 15 seconds, not to
fall below the minimum offset.
JOHNSON CONTROLS
SECTION 1 - DESCRIPTION OF SYSTEM AND FUNDAMENTALS OF OPERATION
The offset is added to the programmed Level Control
setpoint and is displayed as EFFECTIVE REFRIGER-
ANT LEVEL SETPOINT (over the range of 20% to
80%) on both the CONDENSER screen and the RE-
FRIGERANT LEVEL CONTROL screen. This is the
setpoint used to control the level control.
The Orifice can be manually operated from the key-
pad, using this screen. The Refrigerant Level Control
must be enabled by a Service Technician. A complete
description of the Refrigerant level Control operation
are contained in OptiView Control Center Service In-
structions (Form 160.81-M1).
An optional Hot Gas Bypass system allows the chiller
to remain running during extreme light load conditions
by diverting hot refrigerant gas directly from the Oil
Separator to the Evaporator, bypassing the Condenser.
A solenoid valve, located in the bypass line, is opened
and closed under Program control to turn the hot gas
ON and OFF. When the chiller is shutdown, the Hot
Gas Bypass is turned OFF. Each time the chiller is
started, it remains OFF for the first 3 minutes of chiller
operation. Thereafter, it is controlled per the differen-
tial between the Return Chilled Liquid Temperature
and the Leaving Chilled Liquid Temperature setpoint.
This differential is programmed as the Hot Gas ON and
Hot Gas OFF setpoints by a Service Technician. If the
chiller is equipped with the Hot Gas feature, operation
must be enabled by a Service Technician. A complete
description of the Hot Gas Bypass system is contained
in OptiView Control Center Service Instructions (Form
160.81-M1).
To prevent an overcurrent condition when starting the
compressor, the slide valve should be in the unloaded
position. While the unload signal is being applied,
"Slide Valve Unloading Before Shutdown" is dis-
played. To assist the slide valve in returning to the un-
loaded position, an unload signal is applied to it while
the compressor is still running prior to shutting down
on the following shutdowns:
• MULTIUNIT CYCLING - CONTACTS OPEN
• SYSTEM CYCLING - CONTACTS OPEN
• REMOTE STOP
• LEAVING CHILLED LIQUID - LOW
TEMPERATURE
• CONTROL PANEL - SCHEDULE
The duration of the unload signal applied depends on
the software version:
1
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