FORM 150.44-NM4
53
YORK INTERNATIONAL
Power Failure Safety
Whenever power is removed or lost and then reapplied,
auto-restart will occur after a 2 minute anti-recycle timer
elapses. This is the same anti-recycle timer which is
programmable from 5-10 minutes, however it automat-
ically is set to 2 minutes after a power failure.
This safety assures that the motor has a minimum of 2
minutes to cool under any circumstances allowing much
of the internal heating due to starting to be dissipated
before another start occurs.
ANTICIPATION SAFETY CONTROLS
Anticipation controls are built into the software to pre-
vent safety shutdowns by automatically overriding tem-
perature controls if system pressures near safety
thresholds. This allows the chiller to continue to run
under reduced capacity to avoid total loss of cooling
resulting from a lockout on a safety.
Anticipation safeties monitor suction and discharge
pressure and unload the compressors as needed. The
micro will display a message on the STATUS DISPLAY
whenever these controls are in operation.
Suction Pressure Unloading
If suction pressure exceeds the value programmed by
the user (Page 36), the micro will unload the affected
compressor. Automatic reloading will occur when pres-
sure drops 10 PSI below the programmed value. This
value assures that the motor will receive proper cool-
ing from the refrigerant which promotes longer motor
life.
An example of the message displayed when suction
pressure unloading is in effect is shown below:
Discharge Pressure Unloading
If discharge pressure exceeds the value programmed
by the user (Page 35), the micro will unload the af-
fected compressor. Automatic reloading will occur when
pressure drops 60 PSI below the programmed value.
This feature reduces the chance of faulting on the high
discharge pressure cut-out.
On water cooled chillers, this safety reduces the chance
of tripping the relief valve due to a very high rate of rise
in pressure resulting from a controls problem which
would cause condenser water flow to be interrupted.
In this case, the pressure rise is so fast, refrigerant loss
may occur through the relief valve even though the high
pressure cut-out has opened and the compressor is in
the midst of stopping.
An example of the message displayed when discharge
pressure unloadings in effect is shown below:
INTERNAL TIMERS AND PUMPDOWN CONTROLS
ANTI-RECYCLE TIMER
Anytime a compressor shuts down for any reason, re-
start cannot occur until the programmable Anti-recycle
Timer (Page 36) has timed out (timer starts with the
compressor start). Even though the Anti-recycle timer
has timed out, a minimum of 2 minute (2-minute start-up
timer) must always elapse after a compressor stop
before it may again restart.
If a power failure occurs, the anti-recycle timers will
reset to 2 minutes after power is re-applied.
If the anti-recycle timer is preventing a start, the timer
position in seconds may be viewed by pressing the
STATUS key. A sample display is shown below.
ANTI-COINCIDENCE TIMER
The Anti-Coincidence Timer assures that 2 compres-
sors can never start simultaneously. This assures that
excessive current demand will never result. A one min-
ute time delay will always separate compressor starts.
The Anti-Coincidence Timer can be viewed, when it is
active, by pressing the STATUS key. A sample display
is shown below.
PUMPDOWN CONTROLS
Each compressor is controlled by a pumpdown on start-
up feature which eliminates the need for recycling
pumpdown. On start-up, the compressor will pumpdown
to the programmed suction pressure cut-out before the
liquid line solenoid is energized. This assures that liq-
uid slugging does not occur. Manual pumpdown from
the keypad is not possible.
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