Specifications

53
JOHNSON CONTROLS
Form 201.28-NM1.EN.PED/CE (0211)
7
UNIT SAFETIES
Unit Safety Operation
Unit faults are safeties that cause all running compressors
to be shut down, if a safety threshold is exceeded for 3
seconds. Unit faults are recorded in the history buffer
along with all data on the unit and system operating
conditions. Unit faults are auto reset faults where the
unit will be allowed to restart automatically after the
fault condition is no longer present. The only exception
is any of the VSD related unit faults. If any 3 VSD unit
faults occur within 90 minutes, the unit will be locked
out on the last fault. A VSD lockout condition requires
a manual reset using the system switches. Both system
switches must be cycled OFF and ON to clear a VSD unit
lockout fault. If a unit safety is in effect, the message
will be displayed to the operator when the STATUS key
is pressed.
In the descriptions of the fault displays that follow,
the fault message will show a FAULT to indicate that a
system is in a “FAULT” condition and will restart when
the fault clears or LOCKOUT” and will not restart until
the operator clears the fault using the keypad.
If a control panel safety occurs after the VSD fault, but
before the fault is reset, the control panel fault is an ALL
FAULT of the VSD fault, meaning it will be registered
as such in the History because it occurred while the VSD
was shutting down or while the systems were shut down.
All faults do not store operating data at the time of the
fault.
If a “VSD” fault occurs during the fault rampdown or
while the systems are shut down, the VSD fault will be
registered as a new fault. The reason for this is the belief
any VSD fault should be registered with a full account of
the systems data at the time of the fault.
High Ambient Temp Fault
If the ambient temperature rises above 54°C (130°F),
the chiller will shut down with a controlled ramped
shutdown. Restart will automatically occur, if demand
allows, when temperature falls 1.1°C (2°F) below
the cutout (52.9°C[128°F]). This fault cannot cause a
lockout. The fault display message will be present only
during the time when the ambient temperature is causing
a fault condition. A sample display is shown below:
UNIT FAULT:
HIGH AMBIENT TEMP
The unit will also be inhibited from starting any time the
temperature is above 52.9°C (128°F).
Low Ambient Temp Fault
If the ambient temperature falls below the programmable
Low Ambient Temp Cutout the chiller will shut down
with a controlled ramped shutdown. This fault will only
occur if the Low Ambient Cutout is “ENABLED” under
the OPTIONS key. Restart can occur, if demand allows,
when temperature rises 1.1°C (2°F) above the cutout.
This fault cannot cause a lockout. The fault display
message will be present only during the time when the
ambient temperature is causing a fault condition. A
sample display is shown below:
UNIT FAULT:
LOW AMBIENT TEMP
The unit is also inhibited from starting any time the
temperature is below the cutout plus 1.1°C (2°F).
Low Leaving Chilled Liquid Temp Fault
The Low Leaving Chilled Liquid Temp Cutout helps to
protect the chiller from an evaporator freeze-up should
the chilled liquid temp drop below the freeze point. This
situation could occur under low flow conditions or if the
Micro Panel setpoint values are improperly programmed.
Any time the leaving chilled liquid temperature (water
or brine) drops below the programmable cutout point,
the chiller will fault and shutdown with a controlled
ramped shutdown. Restart can occur, if demand allows,
when chilled liquid temperature rises 2.2°C (4°F) above
the cutout. This fault cannot cause a lockout. A sample
shutdown message is shown below:
UNIT FAULT:
LOW LEAVING CHILLED LIQUID TEMP
The unit is inhibited from starting any time the chilled
liquid temperature is below the cutout plus 2.2°C (4°F).
VSD Communications Failure Fault
The VSD Communications Failure is to prevent the
unit from trying to run, if the Chiller Control Board
never initializes communications with the VSD Logic
Board. The unit will also shut down with a controlled
ramped shutdown if the Chiller Control Board loses
communications with the VSD Logic Board while the
chiller is operating.