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The operating sequence described below relates to op-
eration on a hot water start after power has been applied,
such as start-up commissioning. When a compressor
starts, internal timers limit the minimum time before an-
other compressor can start to 1 minute. Time before load-
ing begins is also limited at start. No loading will take
place until a compressor runs for 2-1/2 minutes. After
that, loading will take place every 10 - 120 seconds as
needed. Lag compressor start is also inhibited until the
lead compressor start is also inhibited until the lead com-
pressor reaches a programmable load percentage de-
fined as the Lag Compressor Start Point %.
1. For the chiller system to run, all Manual Reset Cut-
outs must be reset, the Flow Switch must be closed,
any remote cycling contacts must be closed, the SYS-
TEM Switches on the Microboard must be ON, the
Daily Schedule must be scheduling the chiller to run,
and temperature demand must be present.
2. As long as power is applied, the compressor heaters
wil be on and stay on as long as a compressor is not
running.
3. When power is applied to the system, the micropro-
cessor will start a 2 minute timer. This is the same
timer that prevents an instanteous start after a power
failure.
4. At the end of the 2 minute timer, the microprocessor
will check for cooling demand as well as check to see
if any system safeties are exceeded. If all conditions
allow for start, the lead compressor will start unloaded.
YORK INTERNATIONAL
OPERATING SEQUENCE
Coincident with the start, the programmable anti-cycle
timer will be set and begin counting downward to "0".
The liquid line solenoid valve and the Economizer Liq-
uid Supply Solenoid will open after the system pumps
down to the suction pressure cut-out or after the com-
pressor runs for 30 seconds, whichever comes first.
5. After 5 seconds of run time, the microprocessor be-
gins to monitor system operating safeties. These safe-
ties are described in detail in the "Safeties" section of
the manual on Page 106.
6. After 2-1/2 minutes of run time, the lead compressor
will begin to load in intervals of 10 - 120 seconds as
needed to satisfy temperature.
7. The lag compressor may start 1 minute after the lead
compressor starts. However, the lag compressor is
inhibited from the starting until the lead compressor
loads to a % as programmed by the Lag Compressor
Start Point %. This will normally only occur after the
2-1/2 minute period after start where the lead com-
pressor.
8. When the lead compressor loading reaches the Lag
Compressor Start Point %, the lag compressor starts
and will begin to load, if required, after it has run for
2-1/2 minutes.
9. Once both compressors are running, the micro will
attempt to bring the lag compressor up to a load %
equal to that of the lead. Once equalized, the micro
will attempt to load and unload both compressors
equally to satisfy demand and optimizing efficiency.
FORM 201.10-NM1
137
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