Unit Operation - York YCAL0043E Series Installation Operation & Maintenance

CAPACITY CONTROL
To initiate the start sequence of the chiller, all run per-
mis sive inputs must be satisfi ed (fl ow/re mote start/stop
switch), and no chiller or system faults exist.
The fi rst phase of the start sequence is ini ti at ed by the
Daily Schedule Start or a Remote Cycling Device. If the
unit is shut down on the daily sched ule, the chilled wa ter
pump microboard contacts (TB5 3-4) will close when
the daily sched ule start time has been reached. Once
fl ow has been es tab lished and the fl ow switch clos es,
capacity con trol func tions are initiated.
If unit cycling is accomplished with a remote cy cling
device wired in series with the fl ow switch, the chilled
water pump contacts will always be energized as long
as the unit switch is turned on. When the fl ow switch and
remote cycling contacts are closed, the capacity control
func tions will be initiated.
It should be noted that the chilled water pump con tacts
(TB5 3-4) are not required to be used to cy cle the chilled
water pump. However, in all cases the fl ow switch must
be closed to allow unit op er a tion.
The control system will evaluate the need for cool ing
by comparing the actual leav ing or re turn chilled liquid
tem per a ture to the desired setpoint, and reg u late the
leav ing or return chilled liquid tem per a ture to meet that
de sired setpoint.
SUCTION PRESSURE LIMIT CONTROLS
The anticipatory controls are intended to prevent the
unit from ever actually reaching a low-pressure cutout.
Load ing is prevented, if the suction pressure drops
be low 1.15 x suction pressure cutout. Load may reoc-
cur after suc tion pressure rises above the unload point
and a period of one minute elapses. This con trol is only
op er a ble if the op tion al suc tion pres sure transducers
are in stalled.
DISCHARGE PRESSURE LIMIT CONTROLS
The discharge pressure limit controls unload a system
be fore it reach es a safety limit due to high load or dirty
con dens er coils. The micro monitors discharge pres sure
and un loads a system, if fully loaded, by one com pres sor
when dis charge pressure exceeds the programmed
cut out mi nus 15 PSIG. Reloading will occur when the
dis charge pressure on the affected system drops to 85%
of the unload pressure and 10 minutes have elapsed.
This control is only applicable if optional discharge pres-
sure transducers are installed.
YORK INTERNATIONAL

UNIT OPERATION

LEAVING CHILLED LIQUID CONTROL
The setpoint, when programmed for Leaving Chilled
Liq uid Control, is the temperature the unit will control
to within +/- the cooling range. The Setpoint High Lim it
is the Setpoint plus the Cooling Range. The Setpoint
Low Lim it is the Setpoint minus the Cooling Range.
See Fig ure 8. Figure 8 should be utilized to aid in un-
der stand ing the remainder of the description of Leav ing
Chilled Liquid Control.
If the leaving chilled liquid temperature is above the
Setpoint High Limit, the lead com pres sor on the lead
system will be en er gized along with the liquid line so-
le noid. Upon en er giz ing any compressor, the 60 sec ond
Anti-Co in ci dence timer will be initiated.
If after 60 seconds of run-time the leav ing chilled liq-
uid temperature is still above the Setpoint High Lim it,
the next compressor in sequence will be energized.
Ad di tion al compressors will be energized at a rate of
once ev ery 60 sec onds if the chilled liquid tem per a ture
re mains above the Setpoint High Limit and the chilled
liq uid temperature is dropping less than 3°F/min. The
lag system will not be allowed to start a com pres sor until
the lead system has run for 5 minutes.
If the chilled liquid temperature falls below the Setpoint
High Limit but is greater than the Setpoint Low Limit,
load ing and unloading do not occur. This area of con trol
is called the control range.
If the chilled liquid temperature drops to between Set-
point Low Limit and 0.5°F (.28°C) below the Setpoint
Low Lim it, un load ing oc curs at a rate of 60 seconds.
If the chilled liquid tem per a ture falls to a value greater
than 0.5°F (.28°C) be low the Setpoint Low Limit but not
great er than 1.5°F (.83°C) below the Setpoint Low Lim it,
un load ing oc curs at a rate of 20 seconds. If the chilled
liquid tem per a ture falls to a val ue greater than 1.5°F
(.83°C) below the Setpoint Low Lim it, un load ing occurs
at a rate of 30 sec onds. If the chilled liquid temperature
falls below 1°F above the low chilled liquid temperature
cutout, un load ing occurs at a rate of 10 seconds.
Hot gas, if present, will be the fi nal step of capacity. If
temperature remains below the setpoint low limit on the
lowest step of capacity, the micro will close the liquid
line solenoid or EEV, after turning off hot gas, and pump
the system down be fore turning off the last compressor
in a sys tem.
The leaving 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
+/-1.5°F to +/-2.5°F (+/-.83°C to 1.39°C).
FORM 150.62-NM7 (103)
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