Table 92: Safety shutdown messages
Message Description
EVAPORATOR –
LOW PRESSURE
The evaporator pressure, as sensed by the Evaporator Transducer, has
decreased to the shutdown threshold and caused cycling shutdown three times
in a 90 minute period. For water cooling applications, the shutdown threshold
is a fixed value. For Brine cooling applications, the shutdown threshold varies
according to the concentration of the Brine solution. The Brine shutdown
threshold is programmed at the YORK Factory. It should not be changed by
anyone other than a qualified service technician following instructions in
YORK YMC
2
Service Manual (Form 160.84-M2). The chiller can be started after the
evaporator pressure increases to the restart threshold and the CLEAR FAULT key
is pressed.
Shutdown (psig) Restart (psig)
Water Cooling 25.0 25.1
Brine Cooling 6.0 to 25.0 as programmed +0.1> Shutdown threshold
EVAPORATOR –
LOW PRESSURE
– SMART
FREEZE
Smart Freeze protection is activated and has shutdown the chiller because
the evaporator temperature has been below the Smart Freeze threshold for
greater than the allowable number of seconds. If the Evaporator Refrigerant
Temperature sensor RT7 is Enabled, (using procedure in YORK YMC
2
Service
Manual (Form 160.84-M2)), this parameter is used as the evaporator refrigerant
temperature and the freeze threshold is 32.8°F (.4°C). If RT7 is not enabled,
the evaporator refrigerant temperature used is the Evaporator Saturation
Temperature, derived from the Evaporator Pressure Transducer and the freeze
threshold is 34.0°F (1.1°C).
The total count is incremented once for every second the evaporator refrigerant
temperature is below the freeze threshold (but is never decremented below
zero). The number of seconds it will take the chilled liquid to freeze is based on
how far the evaporator refrigerant temperature is below the freeze threshold as
follows:
# seconds to freezing = (4053.7) / (freeze threshold – evap. refrigerant temp.)
Smart Freeze is activated only if the feature has been Enabled by a service
technician (following instructions in YORK YMC
2
Service Manual (Form 160.84-M2))
and the Leaving Chilled Liquid temperature Setpoint is less than 38.0°F (3.3°C).
EVAPORATOR –
TRANSDUCER
OR LEAVING
LIQUID PROBE
A possible defective Evaporator pressure Transducer or Leaving Chilled Liquid
temperature Thermistor has been detected. The pressure and temperature
that these devices are indicating are not in the correct relationship to each
other. The control center converts the evaporator pressure to a Saturated
Temperature value and compares this value to the Leaving Chilled Liquid
temperature (difference = chilled liquid temp – evaporator saturated temp). The
difference should not be outside the range of –2.5°F (1.4°C) to +25.0°F (14.75°C).
If the Transducer and Thermistor are accurate, the Evaporator Saturated
temperature should not be greater than 2.5°F warmer nor greater than 25.0°F
(14.75°C) colder than the leaving chilled liquid temperature. In order to initiate a
shutdown, the difference must be outside the acceptable range continuously for
10 minutes. The chiller can be started after the CLEAR FAULT key is pressed.
127
YMC
2
Mod B with OptiView
™
Control Center
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