York MILLENNIUM YCAS Installation Operation & Maintenance page 138

Micropanel
Low Leaving Liquid Temperature Cut-Out
L E A V I N G L I Q U I D
C U T O U T =
The Low Leaving Liquid Temperature Cutout protects
the evaporator from damage due to ice build up caused
by operation below the chilled liquid freezing point.
If the leaving chilled liquid temperature (water or gly-
col) drops below the cutout point, the chiller will shut
down. The chiller will restart automatically when tem-
perature rises more than 2°C (4ºF) above the cutout
point and cooling demand exists.
If the Dip Switch on the microprocessor board is set for
"Water Cooling" (see Section 3.7, page 113) the cutout
is automatically set at 2°C (36ºF) and cannot be repro-
grammed. If the Switch is set for "Brine Cooling" (gly-
col) the cutout can be programmed between -13 to -
2°C (8.0 - 36.0ºF). The cutout should normally be set to
2°C (4ºF) below the setpoint minus the range, i.e. -2ºC
(setpoint) – 2ºC (range) - 4ºF = 28ºF (see Section 6,
page 123).
To program the Leaving Liquid Temperature Cutout, key
in the required setting and press the Enter key to store
the value into memory and scroll to the next display.
High Motor Current Unload Point
H I G H M O T O R
U N L O A D = 1 0 5 %
The Motor Current Unload point is used to avoid a high
motor current safety shutdown by unloading a compres-
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 ex-
138
T E M P
2 . 2 ° C
C U R R E N T
F L A
cessive current causing compressor shutdown due to
extremely high ambient, high chilled liquid temperature,
and condenser malfunction caused by dirt or fan prob-
lems.
If the programmable limit is set below 100% of full load
current, this feature can be used for "demand limiting".
This is important when demand limiting is critical due to
power requirements or limitations in the building (See
also Section 1.10).
For the first 60 seconds of operation, the unloading safety
is disabled. After this time, if motor current exceeds the
programmed limit, the SYS x CRNT LIMITING mes-
sage will appear on the display and a 1 second unload
pulse will be sent to the slide valve of the affected com-
pressor every 5 seconds, until the motor current drops
below the programmed limit. The message will be re-
moved and additional loading will take place when mo-
tor current drops below 90% of the programmed thresh-
old.
Typically, this setpoint should be set at 100% for
maximum motor protection, programming for
100% is advisable. 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 Timer
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
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.
T I M E R
YORK INTERNATIONAL