Lead / Lag Compressor Selection; Compressor Heater - York MILLENNIUM YCAR0315 Installation Operation & Maintenance

1.21 LEAD / LAG COMPRESSOR SELECTION

The chiller may be set up for AUTO or MANUAL Lead/
Lag. This is accomplished by programming the option
under the Program Key. Details for programming the
Manual/Auto Lead/Lag Selection are discussed in Pro-
gram Key Section 9, page 146.
When AUTO Lead/Lag is utilized, the micro attempts
to balance run time between the two compressors. A
number of conditions can occur which will prevent this
from happening. Factors determining lead/lag selection
and the resulting lead/lag determination are:
1. The micro automatically defaults the lead to SYS 1
and the lag to SYS 2 if both compressors are ready
to start (Anti-recycle Timers timed out) and com-
pressors have equal run time.
2. Individual system run status is not available.
3. If all compressors are ready to start (Anti-recycle
timers timed out), the compressor with the lowest
run hours will start first.
4. If all compressors are waiting to start (Anti-recycle
timers have not timed out), the micro will assign
the lead to the compressor with the shortest anti-
recycle time in an effort to provide cooling quickly.
YORK INTERNATIONAL
5. If the lead compressor is locked out, faulted and
waiting to restart, SYS switch on the microboard is
off, or a run permissive is keeping an individual
system from running, the lag (first lag in YCAR 3-
compressor models) compressor is swapped to the
lead. This is true regardless of whether the lag com-
pressor is ON or OFF.
MANUAL Lead/Lag selection will be automatically
overridden by the micro to allow the lag compressor to
automatically become the lead anytime the selected lead
compressor shuts down due to a lock-out, lead system
faults and is waiting to restart, lead switch on the micro
board is in the OFF position, or if a run permissive is
keeping the lead of the system off. Automatic switchover
in MANUAL mode is provided to try to maintain chilled
liquid temperature as close to setpoint as possible.

1.22 COMPRESSOR HEATER

The compressor heater will be on whenever the respec-
tive compressor is off.
FORM 150.52-NM2 (1001)
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