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Safety shutdown messages
Table 9: Safety shutdown messages
Message
Evaporator – Low
Pressure
Evaporator – Low
Pressure - Smart Freeze
Evaporator – Transducer
Or Leaving Liquid Probe
EVAPORATOR – TRANSDUCER
OR TEMPERATURE SENSOR
44
Description
The evaporator pressure, as sensed by the evaporator transducer, has decreased to the
safety shutdown threshold. For water cooling applications, the safety shutdown threshold
is a fixed value for the respective refrigerant. For brine cooling applications, the safety
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.
Application
Water cooling R-134a
Brine cooling R-134a
The chiller can be started after the evaporator pressure increases to the restart threshold
and the operator presses the Clear Faults button.
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. This
parameter is used as the evaporator refrigerant temperature and the freeze threshold is
32.8°F. 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.
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 and the
Leaving Chilled Liquid Temperature setpoint is <38.0°F.
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 to +25.0°F. If the transducer
and thermistor are accurate, the evaporator saturated temperature should not be > 2.5°F
warmer nor > 25.0°F 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 operator presses the Clear Faults button.
A possible defective Evaporator pressure Transducer or Refrigerant Temperature Sensor
has been detected. The Control Center converts the evaporator pressure to a Saturated
Temperature value and compares this value to the optional Evaporator Refrigerant
Temperature Sensor. If the difference between these temperatures is greater than 3.0°F,
continuously for 1 minute, this shutdown is performed. This check is only performed under
the following conditions:
•
Chiller has been running for at least 10 minutes
•
Evaporator Refrigerant temperature (RT7) has been enabled by a Service technician
•
Not in Brine cooling mode
•
Smart Freeze is enabled
•
Evaporator Temperature Sensor (RT7) or Evaporator Saturation Temperature is
indicating a temperature of <32.0°F
The chiller can be started after the temperatures are within 3.0°F of one another and the
Operator presses the Clear Faults button.
Shutdown (psig)
25.0
6.0 to 25.0 as programmed
Model YD Mod D with OptiView Control Center
Restart (psig)
25.1
+0.1 > Shutdown threshold
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