York YCAV0157 Installation Operation & Maintenance page 205

Pre-charge Low DC Bus Voltage (Software) Fault
The DC bus voltage must reach at least 50 VDC within
four seconds and 500 VDC within 19 seconds after the
pre-charge signal has been asserted. If not, the unit/sys-
tem will shut down on a fault.
This is an auto-restart safety that will lock out on the
3rd fault in 90 minutes. The fault will be a unit fault
for 2 or 3 compressor chillers. The Status display fault
message is shown below:
UNIT YYYYYYYY
PRECHARGE - LOW DC BUS VOLTAGE
The Low DC Bus voltage fault will be a unit fault for 2
and 3 compressor units or a system fault for System 1/3
or 2/4 for 4 compressor units. The reason for this is two
inverter power sections with separate DC Bus circuitry
for each inverter section is utilized on a 4 compressor
unit. One section serves systems 1 and 3 while another
serves systems 2 and 4. The Status display fault mes-
sage is shown below:
SYS X YYYYYYYY PRECHARGE - LOW DC BUS VOLT
X indicates the system and YYYYYYY indicates the
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.
PRE-CHARGE DC BUS VOLTAGE
IMBALANCE (SOFTWARE) FAULT
The 1/2 DC bus voltage magnitude must remain within
+/- 100VDC of the total DC bus voltage divided by two
during the pre-charge interval. If not, the unit/system
shall shut down on a fault.
This safety will lock out on the 1st fault. The fault will
be a unit fault for 2 or 3 compressor units. The Status
display fault message is shown below:
The fault will be a system 1/3 or 2/4 fault for 4 com-
UNIT YYYYYYYY
PRECHARGE - DC BUS VOLTAGE IMBALANCE
JOHNSON CONTROLS
VSD SAFETIES (FAULTS) (CON'T)
pressor units. Two key presses of the STATUS key are
required to show the fault on both systems. The Status
display fault message is displayed below:
X indicates the system and YYYYYYY indicates the
SYS X YYYYYYYY PRECHARGE-BUS VOLT IMBAL
system is in a "LOCKOUT" condition and will not
restart until the operator clears the fault using the key-
pad.
High DC Bus Voltage (Hardware) Fault
The high DC bus voltage trip level is determined by
hardware on the VSD Logic Board and is designed to
trip the unit at 766 +/- 30 VDC. If the DC bus exceeds
this level, the unit/system will fault and shut down im-
mediately.
This safety is an auto-restart safety that will lock out
on the 3rd fault in 90 minutes. The fault will be a unit
fault for 2 or 3 compressor units. Two ket presses of
the STATUS KEY are required to show the fault on
both systems. Below is the control panel Status display
fault message:
UNIT YYYYYYYY
HIGH DC BUS VOLTAGE
The fault will be a system 1/3 or 2/4 fault on 4 compres-
sor units. Below is the Status display fault messages for
all systems: Two key presses of the STATUS Key are
required to show the fault on both systems.
SYS X YYYYYYYY HIGH DC BUS VOLTAGE
X indicates the system and YYYYYYY indicates the
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.
FORM 201.21-NM1 (1223)
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