YORK INTERNATIONAL
96
FORM 150.62-NM7 (103)
FIG. 8 – LEAVING WATER TEMPERATURE CONTROL EXAMPLE
LEAVING CHILLED LIQUID CONTROL OVERRIDE
TO REDUCE CYCLING
To avoid compressor cycling the micro will adjust the
setpoint upward temporarily. The last run time of the
system will be saved. If the last run time was greater than
5 minutes, no action is to be taken. If the last run time
for the lead system was less than 5 minutes, in crease
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 5 minutes, the
setpoint adjust will be set back to 0. This will occur while
the sys tem is still running.
FIG. 7 – SETPOINT ADJUST
Leaving Water Temp. Control – Compressor Staging
Setpoint = 46.0°F (7.8°C) Range = +/- 2°F(1.1°C)
30 sec. control range 60 sec.
unloading (no compressor staging) loading
44.0°F 46.0°F 48.0°
(6.7°C) (7.8°C) (8.9°C)
Low Limit Setpoint High limit
LWT
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
Unit Controls
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 com-
pres sors to match the cooling load. The chill er 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 com pres sors off) when the re-
turn water temperature is equal to the Cool ing Setpoint.
(See sample in Table 23) At return water tem per a tures
be tween the Cool ing, and Cool ing Setpoint plus Range,
com pres sor load ing and unloading will be de ter mined
by the for mu las in Ta ble 24 or Table 25.
Return Chilled Liquid Control MUST
only be used when constant chilled
liq uid fl ow is ensured.
The RANGE MUST always be pro-
grammed to equal the temperature
drop across the evaporator when the
chill er is “fully load ed”. Otherwise,
chilled liquid tem per a ture will over or
under shoot.
Normal loading will occur at intervals of 60 seconds ac-
cord ing to the temperatures de ter mined by the for mu las.
Un load ing will occur at a rate of 30 seconds ac cord ing to
the temperatures determined in the for mu las.
The return chilled liquid setpoint is pro gram ma ble from
40°F to 70°F (4.4°C to 21.1°C) in water chill ing mode
and from 10°F to 70°F (-12.2°C to 21.1°C) in glycol
chill ing mode. In both modes, the cooling range can be
from 4°F to 20°F (2.2° to 11.1°C).
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