York Millennium YCAS Series Installation Operation & Maintenance page 171

sor, if current draw approaches the maximum limit cut-
out value. The chiller can then continue to run auto-
matically at reduced capacity until the cause of the ex-
cessive current is attended to.
The micro will accept between 30 - 105% for the un-
load point. The motor current safety will shut the com-
pressor down whenever current exceeds 115%.
If the programmable limit is set between 100% and
105% of full load current, this safety will protect against
excessive current causing compressor shutdown due to
extremely high ambient, high chilled liquid tempera-
ture, and condenser malfunction caused by dirt or fan
problems.
If the programmable limit is set below 100% of full
load current, this feature can be used for "demand lim-
iting". This is important when demand limiting is criti-
cal due to power requirements or limitations in the build-
ing (See also Section 1.10).
For the first 60 seconds of operation, the unloading
safety is disabled. After this time, if motor current ex-
ceeds the programmed limit, the SYS x CRNT LIMIT-
ING message will appear on the display and a 1 second
unload pulse will be sent to the slide valve of the af-
fected compressor every 5 seconds, until the motor cur-
rent drops below the programmed limit. The message
will be removed and additional loading will take place
when motor current drops below 90% of the pro-
grammed threshold.
Typically, this setpoint should be set at 100% for
maximum motor protection. Programming for
100% is recommended. When programming values
below 100% use of a leading "0" is required, e.g. 085%.
To program the High Motor Current Unload, key in the
required setting and press the Enter key to store the
value into memory and scroll to the next display.
Anti-Recycle Time
A N T I R E C Y C L E
= 6 0 0 S E C S
The Anti-Recycle Timer controls the minimum time
between starts for each compressor. This is the time
available for the heat build up caused by inrush current
at start to be dissipated before the next start. Insuffi-
cient cooling time between starts can cause heat build
up and motor damage. A fast compressor start response
is needed in some applications and not in others. Al-
though the minimum setting allowed on this timer will
YORK INTERNATIONAL
avoid excessive heat build up, adjusting the timer for
the longest period acceptable in each application will
reduce cycling and maximize motor life. 600 seconds
is recommended.
The micro will accept a range of programmable values
between 300 - 600 seconds.
To program the Anti-Recycle Time, key in the required
setting and press the Enter key to store the value into
memory and scroll to the next display.
Local/Remote Communications
The panel can be programmed for "Local" or "Remote"
communications. "Local" mode allows monitoring
through the RS-485 port only. "Remote," allows an ex-
ternal device such as an ISN or Remote Control Center
to change setpoints and programming points.
The !#
mote. The ENTER Key must be pressed to save the
selection in memory.
Imperial/SI Units Display
This allows the operator to select the display messages
to display Imperial Units (PSIG, F, etc.) or SI (Scien-
tific International, Bars, C, etc.).
The !#
units. The ENTER Key must be pressed to save the
selection in memory.
Automatic/Manual "Lead/Lag"
The chiller may be selected for manual lead/lag or au-
T I M E R
tomatic lead/lag. In some cases the operator may want
to manually select the system that is desired to be the
lead system. In most cases, automatic lead/lag is se-
lected to allow the micro to attempt to balance run time
between the system. Details of manual and automatic
lead / lag operation are outlined in Section 1.21.
The !#
Manual lead/lag. The ENTER key must be pressed to
save the selection in memory.
L O C A L / R E M O T E
L O C A L
!# !# !# keys are used to change from Local to Re- !#
D I S P L A Y
I M P E R I A L
!# !# !# !# keys are used to change from Imperial to SI
L E A D / L A G
A U T O M A T I C
!# keys are used to change from Automatic to !# !#
!#
FORM 201.18-NM4
M O D E
U N I T S
C O N T R O L
171
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