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SECTION 7 - OPERATION
and have been successfully initialized, the Chiller
Control Board will not request them again. If the com-
ms connection fails to occur and a reply from the VSD
Logic Board does take place in 8 seconds, the Chiller
Control Board will prevent the chiller from operating
and a fault message will be displayed.
During normal operation, if the control panel Chiller
Control Board receives no valid response to messages
for 8 seconds, the unit will shut down all compressors
on a Comms fault. The Chiller Control Board will con-
tinue to send messages to the VSD while faulted. The
unit will be inhibited from starting until communica-
tions is established. The fault will automatically reset
when the Chiller Control Board receives a valid re-
sponse from the VSD for a data request. The following
is an example of a Comms Failure fault message:
UNIT YYYYYYYY
VSD COMMUNICATIONS FAILURE
System safeties, faults
System safety (fault) operation
System safeties are faults that cause individual systems
to be shut down if a safety threshold is exceeded for 3
seconds. System faults are auto reset faults in that the
system will be allowed to restart automatically after the
120 second anti-recycle timer times out. The only ex-
ception is after any 3 faults on the same system occur
within 90 minutes, that system will be locked out on
the last fault. The lockout condition requires a manual
reset using the system switch. The respective system
switch must be cycled OFF and ON to clear the lockout
fault.
When multiple systems are operating and a system
fault occurs, the running systems will ramp down and
the faulted system will be shut OFF and the previously
operating will restart if required after the fault clears
and/or the 120 second anti-recycle timer times out.
In the descriptions of the fault displays that follow, the
fault message will show a YYYYYYYY to indicate
that a system is in a "FAULT" condition and will re-
start when the fault clears, or "LOCKOUT" and will
not restart until the operator clears the fault using the
keypad. If a system safety is in effect, the message will
be displayed to the operator when the STATUS key is
pressed.
In some cases, a control panel fault will occur after
a VSD fault, possibly during system shutdown or at
some later time. This is known as an "ALL FAULT"
126
and these faults will be recorded as such under the
HISTORY information stored at the instant of the pri-
mary fault. In some cases, this information may be
valuable in troubleshooting the primary fault. An ex-
ample of the "ALL FAULT" history message as shown
in the All Fault Data on Page 143 under the HIS-
TORY key. When an "ALL FAULT" occurs, associated
history information will not be stored. If an additional
fault does not occur, the "ALL FAULTS" display will
indicate NONE.
In cases where a VSD fault occurs during the ramp-
down of a control panel fault (that is, low suction pres-
sure, low water temp, and so on), the VSD fault will
be stored as a new fault with the associated fault in-
formation stored at the instant the VSD fault occurred
(that is, IGBT Gate Drive, Single Phase Input, VSD CT
Plug, and so on). The control panel fault that occurred
before the VSD fault will be stored with the associ-
ated complete data related to the fault as a numerically
lower numbered history in the history buffers.
High discharge pressure cutout (software)
fault
The High Discharge Pressure Cutout is a software
fault. A system will fault and shut down with a con-
trolled ramped shutdown on high discharge pressure
when the discharge pressure rises above 22.4 barg (325
psig) for 0.5 seconds. The system will be allowed to
restart when the discharge pressure falls to 20.3 barg
(295 psig). The system will also be inhibited from
starting if the pressure is above 20.3 barg (295 psig).
The following is the fault message for this safety:
SYS X YYYYYYYY HIGH DISCHARGE PRESSURE
The X indicates the system and YYYYYYYY in-
dicates the system is in a FAULT condition and will
restart when the 120 second anti-recycle timer times
out, or LOCKOUT and does not restart until the
operator clears the fault using the keypad.
High discharge pressure cutout (HPCO)
(hardware) fault
The mechanical high pressure cutout protects the sys-
tem from experiencing dangerously high discharge
pressure. A system will fault and shut down immediate-
ly when the mechanical high pressure cutout contacts
open. The fault occurs immediately and does not wait 3
seconds, which is common in most system faults.
Form 201.28-NM1.1
Issue date: 08/06/2021
JOHNSON CONTROLS
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