Unit Operating Sequence - York YCAL0043E Series Installation Operation & Maintenance

The operating sequence described below relates to op-
er a tion on a hot water start after power has been ap plied,
such as start-up commissioning. When a com pres sor
starts, in ter nal tim ers limit the min i mum time before
an oth er com pres sor can start to 1 minute.
1. For the chiller system to run, the Flow Switch must
be closed, any remote cycling contacts must be
closed, the Daily Schedule must not be sched ul ing
the chill er off, and tem per a ture demand must be
present.
2. When power is applied to the system, the mi cro pro -
ces sor will start a 2 minute timer. This is the same
timer that prevents an instantaneous start after a
pow er failure.
3. At the end of the 2 minute timer, the mi cro pro ces sor
will check for cooling demand. If all con di tions al low
for start, a compressor on the lead sys tem will start
and the liq uid line solenoid will open or the EEV
will begin to operate (EEV equipped chillers only).
Co in ci dent with the start, the anti-co in ci dent tim er
will be set and be gin count ing down ward from "60"
sec onds to "0" sec onds.
If the unit is programmed for Auto Lead/Lag, the
sys tem with the shortest average run-time of the
com pres sors will be assigned as the "lead" sys tem.
A new lead/lag as sign ment is made when ev er all
sys tems shut down.
4. Several seconds after the compressor starts, that
sys tems fi rst condenser fan will be cycled on (out-
YORK INTERNATIONAL

UNIT OPERATING SEQUENCE

door air temperature > 25°F (-4°C) or discharge
pres sure). See the sec tion on Op er at ing Con trols
for de tails con cern ing con dens er fan cycling.
YCAL0287 – YCAL0377 cycle fans on discharge
pressure only.
5. After 1 minute of compressor run time, the next com-
pres sor in sequence will start when a sys tem has to
load. Additional com pres sors will be start ed at 60
second intervals as need ed to sat is fy tem per a ture
setpoint.
6. If demand requires, the lag system will cycle
on with the same timing sequences as the lead
system after the lead system has run for fi ve min-
utes. Re fer to the sec tion on Ca pac i ty Con trol for
a de tailed ex pla na tion of sys tem and com pres sor
stag ing.
7. As the load decreases below setpoint, the com pres -
sors will be shut down in sequence. This will oc cur
at in ter vals of either 60, 30, or 20 sec onds based
on water temperature as compared to setpoint, and
con trol mode. See the section on Capacity Control
for a de tailed ex pla na tion.
8. When the last compressor in a "system" (two or
three compressors per system), is to be cycled off,
the sys tem will initiate a pump-down. Each "sys tem"
has a pump-down fea ture upon shut-off. On a non-
safe ty, non-unit switch shut down, the LLSV will be
turned off or the EEV will close (EEV equipped chill-
ers only), and the last com pres sor will be al lowed
to run until the suc tion pres sure falls be low the suc-
tion pres sure cut out or for 180 sec onds, whichever
comes fi rst.
FORM 150.62-NM7 (103)
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