FORM 150.60-NM4
YORK INTERNATIONAL
55
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 automati-
cally 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 thresh-
olds. This allows the chiller to continue to run under re-
duced capacity to avoid total loss of cooling resulting
from a lockout on a safety.
Anticipation safeties monitor suction and discharge pres-
sure and unload the compressors as needed. The micro
will display a message on the STATUS DISPLAY when-
ever these controls are in operation.
Suction Pressure Unloading
If suction pressure exceeds the value programmed by
the user (Page 37), 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 cooling
from the refrigerant which promotes longer motor life.
An example of the message displayed when suction pres-
sure unloading is in effect is shown below:
Discharge Pressure Unloading
If discharge 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 60 PSI below the programmed value. This
feature reduces the chance of faulting on the high dis-
charge 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 pres-
sure 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 Anit-recycle
Timer (Page 37) has timed out (timer starts with the com-
pressor 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 be-
fore it may again restart.
If a power failure occurs, the anti-recycle timers will re-
set 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 STA-
TUS key. A sample display is shown below.
ANTI-COINCIDENCE TIMER
The Anti-Coincidence Timer assures that 2 compressors
can never start simultaneously. This assures that ex-
cessive current demand will never result. A one minute
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 liquid
slugging does not occur. Manual pumpdown from the
keypad is not possible.
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