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SECTION 7 - OPERATION
On power-up, the Chiller Microprocessor Board will
attempt to initialize communications with the VSD
Logic Board. The control panel will request data from
the VSD, which includes the number of compressors
and the VSD software version. Once these data points
have been received by the Chiller Control Board, and
have been successfully initialized, the Chiller Control
Board will not request them again. If the comms con-
nection fails to occur and a reply from the VSD Logic
Board does take place in 8 seconds, the Chiller Con-
trol 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. Shown below
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
exception is after any 3 faults on the same system oc-
cur 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 indi-
cate that a system is in a “FAULT” condition and will
FORM QTC4-NM1
ISSUE DATE: 4/2/2018
restart 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”
and these faults will be recorded as such under the
HISTORY information stored at the instant of the
primary fault. In some cases, this information may
be valuable in troubleshooting the primary fault. An
example of the “ALL FAULT” history message is
shown on page 132 under the HISTORY key. When
an “ALL FAULT” occurs, associated history infor-
mation 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 (i.e.: low suction pres-
sure, low water temp, etc.), the VSD fault will be
stored as a new fault with the associated fault informa-
tion stored at the instant the VSD fault occurred (for
example, IGBT Gate Drive, Single Phase Input, VSD
CT Plug, etc.). The control panel fault that occurred
prior to 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 fault message for this safety is shown below:
SYS X YYYYYYYY HIGH DISCHARGE PRESSURE
The X indicates the system and YYYYYYYY
indicates the system is in a “FAULT” condition and
will restart when the 120 second anti-recycle timer
times out, or “LOCKOUT” and will not restart until
the operator clears the fault using the keypad.
Page 110
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