York YK-EP Operation And Maintenance Manual page 209

Table 205: Evaporator pressure thresholds
Water Cooling - R22
- R134a
Brine Cooling - R22
- R134a
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 OptiView Control Center – Service Instructions (Form 160.54-M1)), 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:
Smart Freeze is activated only if the feature has been enabled by a Service Technician (following
instructions in OptiView Control Center – Service Instructions (Form 160.54-M1)) and the Leaving
Chilled Liquid Temperature Setpoint is less than 38.0°F.
Evaporator – Transducer Or Leaving Liquid Probe
A possible defective Evaporator Pressure transducer or Leaving Chilled Liquid temperature
transmitter 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 equals chilled liquid temp minus evaporator saturated temp). The
difference should not be outside the range of –2.5°F to +25.0°F. If the transducer and transmitter
are accurate, the Evaporator Saturated temperature should not be greater than 2.5°F warmer
nor greater than 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 WARNING RESET button.
Evaporator – Transducer Or Temperature Sensor
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
YK-EP Style B Centrifugal Chiller
Shutdown (PSIG)
54.3
25.0
25.0 to 54.3 as programmed
6.0 to 25.0 as programmed
number of seconds
=
to freezing
Restart (PSIG)
+0.1 more than Shutdown threshold
+0.1 more than Shutdown threshold
(4053.7)
freeze threshold -
evap. refrigerant temp.
54.4
25.1
209