Unit Operating Sequence - York YCAL Series Installation Operation & Maintenance

SECTION 5 - COMMISSIONING
The operating sequence described below relates to op-
eration on a hot water start after power has been ap-
plied, such as start-up commissioning. When a com-
pressor starts, internal timers limit the minimum time
before another compressor 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 scheduling
the chiller off, and temperature demand must be
present.
2. When power is applied to the system, the micropro-
cessor will start a 2 minute timer. This is the same
timer that prevents an instantaneous start after a
power failure.
3. At the end of the 2 minute timer, the microproces-
sor will check for cooling demand. If all conditions
allow for start, a compressor on the lead system will
start and the liquid line solenoid will open or the
EEV will begin to operate (EEV equipped chillers
only). Coincident with the start, the anti-coincident
timer will be set and begin counting downward from
"60" seconds to "0" seconds.
If the unit is programmed for Auto Lead/Lag, the
system with the shortest average run-time of the
compressors will be assigned as the "lead" system.
A new lead/lag assignment is made whenever all
systems shut down.
44

UNIT OPERATING SEQUENCE

4. Several seconds after the compressor starts, that sys-
tems first condenser fan will be cycled on (outdoor
air temperature more than 25°F (-4°C) or discharge
pressure). See SECTION 7 - UNIT CONTROLS for
details concerning condenser fan cycling.
5. After 1 minute of compressor run time, the next
compressor in sequence will start when a system
has to load. Additional compressors will be started at
60 second intervals as needed to satisfy temperature
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 five minutes.
See CAPACITY CONTROL for a detailed explana-
tion of system and compressor staging.
7. As the load decreases below setpoint, the compres-
sors will be shut down in sequence. This will occur
at intervals of either 60, 30, or 20 seconds based
on water temperature as compared to setpoint, and
control mode. See CAPACITY CONTROL for a
detailed explanation.
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 "system" has a
pump-down feature upon shut-off. On a non-safety,
non-unit switch shutdown, the LLSV will be turned
off or the EEV will close (EEV equipped chillers
only), and the last compressor will be allowed to
run until the suction pressure falls below the suc-
tion pressure cutout or for 180 seconds, whichever
comes first.
FORM 150.66-NM3
ISSUE DATE: 09/25/2020
JOHNSON CONTROLS