York Millennium YCAJ150, Installation Operation & Maintenance, Page: 75 / 116

FORM 150.65-NM4
75 YORK INTERNATIONAL
26000A
FIG. 23 – LOCATION OF THE MICROPROCESSOR BOARD
FIG. 24 – ALARM CONTACT CONNECTION LOCATION
LD02092
26001A
SYSTEM SWITCHES 1-4
ON MICROPROCESSOR BOARD
MICROPROCESSOR
BOARD
When AUTO Lead/Lag is utilized, the micro attempts to
balance run time between the two compressors. A num-
ber of conditions can occur which will prevent this from
happening. Factors determining lead/lag selection and
the resulting lead/lag determination are discussed be-
low:
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. If both compressors are ready to start (Anti-recycle
Timers timed out), the compressor with the lowest
run hours will start first.
3. If both compressors are waiting to start (Anti-recycle
Timers are 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.
4. If the lead compressor is locked out, faulted and
waiting to restart, SYS switch on the micro board is
off, or a run permissive is keeping an individual sys-
tem from running, the lag compressor is swapped to
the lead. This is true regardless of whether the lag
compressor is on or off.
If MANUAL Lead/Lag is selected, an external “dry” con-
tact (switch) must be wired into the chiller. This contact
is field supplied. With the contact open, SYS 1 is placed
in the lead. When the contact is closed, SYS 2 will be
the lead system.
Manual Lead/Lag selection will be automatically overrid-
den by the micro to allow the lag compressor in a mod-