York YCWS0313SC, Installation, Operation And Maintenance Manual, Page: 43 / 104

FORM 201.24-NM2
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YORK INTERNATIONAL
An adjustable timer allows for the motor cooling, but
gives the user the ability to extend the anti-recycle timer
to cut down on cycling. In some applications, faster
compressor start response is necessary and shorter anti-
recycle times are required. These needs should be kept
in mind but whenever possible the timer should be ad-
justed for the longest period of time tolerable.
600 seconds is recommended, although 300 seconds
provides adequate motor cooling time. Longer periods
will allow more heat dissipation, reduce cycling, and
possibly increase in motor life.
1.21 ANTI-COINCIDENCE TIMER
The anti-coincidence timer prevents 2 compressors start-
ing simultaneously. This assures that the inrush current is
kept to a minimum. A 60 second time delay will always
separate motor starts. This timer is not programmable.
1.22 COMPRESSOR HEATER CONTROL
Each compressor has its own heater. The heater will be
off whenever the compressor is running. When the com-
pressor shuts off, the heater will be switched on and
stay on for 5 minutes. After 5 minutes has elapsed, the
heater will switch off if the discharge temperature rises
above 66°C and will come on when the discharge tem-
perature is equal to or less than 66°C.
1.23 PUMPDOWN (LLSV) CONTROL
Each compressor undergoes a pump down cycle on
start-up and shutdown. This assures that liquid refrig-
erant does not enter the compressor on start-up, elimi-
nating the need for recycling pump down, saving en-
ergy and reducing compressor starts and wear.
On start-up, the controls unload the compressor and
the system either pumps down to the low suction pres-
sure cutout setting or pumps down for 60 seconds
(whichever comes first) after which the liquid line so-
lenoid valve is energized and normal operation starts.
On shutdown, the microprocessor controls unload the
compressor and the liquid line solenoid valve and
economizer/motor cooling liquid supply solenoid valve
are de-energized. The compressor continues to operate
until it either pumps down to the low suction pressure
cutout setting or for 180 seconds, whichever comes first.
Pump down occurs on “normal” shutdowns where cool-
ing demand has been satisfied or when a system switch
is turned off, a flow switch opens, run permissive is
lost or a ‘Daily Schedule’ or a remote shutdown is called
for. No pump-down will occur on a safety shutdown.
1.24 LEAD/LAG COMPRESSOR SELECTION
The chiller may be set up for ‘AUTO’ or ‘MANUAL’
lead/lag. This is accomplished by programming the op-
tion under the ‘PROGRAM KEY’.
When ‘AUTO’ lead/lag is used, the microprocessor at-
tempts to balance run time between the compressors.
A number of conditions can occur which will prevent
this from happening. Factors determining lead/lag se-
lection and the resulting lead/lag determination are:
• The microprocessor automatically defaults the lead
to system 1 and the lag to system 2 if both com-
pressors are ready to start (Anti-recycle Timers
timed out) and compressors have equal run time.
• If all compressors are ready to start (Anti-recycle
timers timed out), the compressor with the lowest
run hours will start first.
• If all compressors are waiting to start (Anti-recycle
timers have not timed out), the microprocessor will
assign the lead to the compressor with the shortest
anti-recycle time to provide cooling quickly.
• If the lead compressor is locked out, faulted and
waiting to restart, the system switch on the AMB
board is ‘OFF’, or a run permissive is keeping an
individual system from running, the lag compres-
sor is swapped to the lead. This is true regardless
of whether the lag compressor is ‘ON’ or ‘OFF’.
‘MANUAL’ lead/Lag selection will be automatically
overridden by the microprocessor to allow the lag com-
pressor to automatically become the lead anytime the
selected lead compressor shuts down due to a lockout,
lead system faults and is waiting to restart, lead switch
on the AMB board is in the ‘OFF’ position, or if a run
permissive is keeping the lead of the system off.
Automatic switch over in ‘MANUAL’ mode is provided
to try to maintain chilled liquid temperature as close to
setpoint as possible.
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