Specifications

YORK INTERNATIONAL 31
FORM 160.48-O1
chilled water temperature. Cooling tower fan cycling
will normally provide adequate control of the entering
condenser water temperature on most installations.
CHECKING OPERATION
During operation, the following conditions should be
periodically checked:
1. On starting, the prerotation vanes should remain
closed.
2. Be sure the oil pump is operating while unit is running.
3. Check Oil Pressure display. A gradual decrease in
bearing oil pressure of 5 to 10 PSI (with constant
suction and discharge pressures) may be an indica-
tion of a dirty filter. The filter should be replaced when
pressure loss is 30% or more of the original pres-
sure. The actual bearing oil pressure will vary with
compressor suction and discharge pressures. When
a new system is first operated under normal full load
conditions, the bearing oil pressure should be re-
corded as a reference point with which to compare
subsequent readings.
OPERATING LOG SHEET
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.
FIG. 19 - MINIMUM ENTERING CONDENSING
WATER TEMPERATURE
tain the leaving chilled liquid temperature setpoint. The
prerotation vanes are modulated by an actuator under
the control of the microprocessor board or logic section
of the Variable Speed Drive. The vane control routine
employs proportional plus derivative (rate) control ac-
tion. A drop in chilled liquid temperature will cause the
actuator to close the prerotation vanes (and also de-
creases the speed of the motor if equipped with a Vari-
able Speed Drive) to decrease chiller capacity. When
the chilled liquid temperature rises, the actuator will open
the prerotation vanes and increase the compressor
motor speed of the chiller (if controlled by the Variable
Speed Drive), to increase the capacity of the unit.
However, the current draw (amperes) by the compres-
sor motor cannot exceed the setting of the “% CUR-
RENT LIMIT” at any time during the unit operation, since
the MicroComputer Control Center 40 to 100% three
phase peak current limit software function, plus the 3
phase 100% solid state overload current limiter (CM-2)
on Electro-Mechanical Starter applications or the solid
state starter current limit function will override the tem-
perature control function (or the logic section of the
Variable Speed Drive) and prevent the prerotation
vanes from opening beyond the “% CURRENT LIMIT”
setting.
If the load continues to decrease, after the prerotation
vanes are entirely closed, the chiller will be shut down
by the Low Water Temperature control (LWT) function
which is displayed on the Control Center as:
MON 10:30 AM – LOW WATER TEMPERATURE – AUTOSTART
- or -
MON 03:50 PM – LOW WATER TEMPERATURE – VSD AUTOSTART
This occurs when the leaving water temperature falls
to 4°F below setpoint or 36°F, whichever is higher. The
LWT is part of the Micro Board or the capacity control
board (part of the logic section of the Variable Speed
Drive).
NOTE: If the temperature setpoint has been repro-
grammed within the last 10 minutes, the LWT
cutout is 36°F for 10 minutes.
Condenser Water Temperature Control
The YORK Millenium chiller is designed to use less
power by taking advantage of lower than design tem-
peratures that are naturally produced by cooling towers
throughout the operating year. Exact control of con-
denser water, such as a cooling tower bypass, is not
necessary for most installations. The chiller requires only
that the minimum condenser water temperature be no
lower than the value determined by referring to Fig. 19.
At start-up the entering condenser water temperature
may be as much as 25°F colder than the standby return
LD00466