York YCAL0014E Series, Installation Operation & Maintenance

Page: 114 / 212

JOHNSON CONTROLS
114
FORM 150.62-NM8 (1020)
UNIT OPERATION
If the chilled liquid temperature drops to between
Setpoint Low Limit and 0.5°F (.28°C) below the
Setpoint Low Limit, unloading occurs at a rate of 60
seconds. If the chilled liquid temperature falls to a
value greater than 0.5°F (.28°C) below the Setpoint
Low Limit but not greater than 1.5°F (.83°C) below
the Setpoint Low Limit, unloading occurs at a rate of
20 seconds. If the chilled liquid temperature falls to a
value greater than 1.5°F (.83°C) below the Setpoint Low
Limit, unloading occurs at a rate of 30 seconds. If the
chilled liquid temperature falls below 1°F above the low
chilled liquid temperature cutout, unloading occurs at a
rate of 10 seconds.
Hot gas, if present, will be the final step of capacity.
If temperature remains below the Setpoint Low Limit
on the lowest step of capacity, the microprocessor will
close the liquid line solenoid or EEV, after turning off
hot gas, and pump the system down before turning off
the last compressor in a system.
The Leaving Chilled Liquid Setpoint is programmable
from 40°F to 70°F (4.4°C to 21.1°C) in water chilling
mode and from 10°F to 70°F (-12.2°C to 21.1°C) in
glycol chilling mode. In both modes, the cooling range
can be from plus or minus1.5°F to plus or minus2.5°F
(plus or minus.83°C to 1.39°C).
Leaving Chilled Liquid Control Override to
Reduce Cycling
To avoid compressor cycling the I/O Board will adjust
the setpoint upward temporarily. The last run time of the
system will be saved. If the last run time was greater than
five minutes , no action is to be taken. If the last run time
for the lead system was less than five minutes , increase
the Setpoint High Limit according to the chart at right,
with a maximum value allowed of 50°F.
If adding the setpoint adjust value to the Setpoint High
Limit causes the Setpoint High Limit to be greater than
50°F, the Setpoint High Limit will be set to 50°F, and the
difference will be added to the Setpoint Low Limit.
Once a system runs for greater than five minutes , the
setpoint adjust will be set back to 0. This will occur
while the system is still running.
RETURN CHILLED LIQUID CONTROL
(Can be used on Dual System 4, 5 & 6 Comp Units
Only)
Return Chilled Liquid Control is based on staging the
compressors to match the cooling load. The chiller will
be fully loaded when the return water temperature is
equal to the Cooling Setpoint plus the range. The chiller
will be totally unloaded (all compressors off) when the
return water temperature is equal to the Cooling Setpoint
(see sample in Table 24). At return water temperatures
between the Cooling, and Cooling Setpoint plus range,
compressor loading and unloading will be determined
by the formulas in Table 25 or Table 26.
Return Chilled Liquid Control MUST
only be used when constant chilled
liquid flow is ensured.
The RANGE MUST always be pro -
grammed to equal the temperature
drop across the evaporator when the
chiller is fully loaded. Otherwise,
chilled liquid temperature will over or
under shoot.
FIG. 7 – SETPOINT ADJUST
0 1 2 3 4 5 6
LAST RUN TIME OF LEAD SYSTEM (MINUTES)
SETPOINT
ADJUST
(DEG. F)
6
5
4
3
2
1
0
LD07617A
FIG. 8 – LEAVING WATER TEMPERATURE
CONTROL EXAMPLE
44.0 ºF
(6.7 ºC)
Low Limit
46.0 ºF
(7.8 ºC)
Setpoint
48.0 ºF
(8.9 ºC)
High Limit
Leaving Water Temp. Control - Compressor Staging
Setpoint = 46.0 ºF (7.8 ºC) Range = +/-2 ºF (1.1 ºC)
30 sec.
unloading
60 sec.
loading
Contol Range
(no compressor staging)
LWT
LD14404