JOHNSON CONTROLS
126
FORM 160.78-O2
ISSUE DATE: 5/22/2017
SECTION 2 - OPTIVIEW CONTROL CENTER INTRODUCTION
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 xed value. For Brine cool-
ing 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 qualied Service Technician following in-
structions in YORK YMC
2
Service Manual (Form 160.78-M2). The chiller can be started
after the evaporator pressure increases to the restart threshold and the CLEAR FAULT
key is pressed.
SHUTDOWN
SHUTDOWN
(PSIG)
RESTART
(PSIG)
Water Cooling
-R134a
25.0 25.1
Brine Cooling
-R134a
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 evapo-
rator 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 160.78-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 tem-
perature is below the freeze threshold (but is never decremented below zero). The num-
ber 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 160.78-M2)) and the Leav-
ing 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 tempera-
ture 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 – evap-
orator 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 shut-
down, the difference must be outside the acceptable range continuously for 10 minutes.
The chiller can be started after the CLEAR FAULT key is pressed.
TABLE 9 - SAFETY SHUTDOWN MESSAGES (CONT'D)
To Next Page
Loading...
