Specifications

55
JOHNSON CONTROLS
Form 201.28-NM1.EN.PED/CE (0211)
7
Some faults will be unit faults; other faults will be
system (specific compressor or compressor pairs) faults,
depending upon the number of compressors in the chiller.
Most faults will shut down the unit/ system and allow
restart once the fault clears and the 120 sec anti-recycle
timer times out. These faults will allow up to 3 faults in
90 minutes before locking out the unit/system. Other
faults lock out the unit/system after only a single fault.
Details on individual faults are provided in the following
explanations.
A start inhibit will take place if a VSD fault condition
exists and a compressor that is not running is called
to start. The start inhibit will be cleared when the
fault condition goes away and the compressor will be
permitted to start.
Pre-charge Low DC Bus Voltage (Software)
Fault
The DC bus voltage must reach at least 41 Vdc within
four seconds and 414 Vdc within 19 seconds after the
pre-charge signal has been asserted. If not, the unit/
system 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. The
Status display fault message is shown below:
UNIT FAULT:
PRECHARGE - LOW DC BUS VOLTAGE
Pre-charge DC Bus Voltage Imbalance (Soft-
ware) Fault
The 1/2 DC bus voltage magnitude must remain within
+/- 100 Vdc 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. The Status display fault message is shown
below:
UNIT FAULT:
PRECHARGE - DC BUS VOLTAGE IMBALANCE
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 will fault and shut down immediately.
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.
Below is the control panel Status display fault message:
UNIT FAULT:
HIGH DC BUS VOLTAGE
Low DC Bus Voltage (Software) fault
The low DC bus voltage trip level is set at 414 Vdc. If
the DC bus drops below this level the unit will fault and
immediately shut down.
The low DC bus voltage cutout is an auto-restart safety
that will lock out on the 3rd fault in 90 minutes. The
fault is a unit fault. Below is an example of the Status
display fault message:
UNIT FAULT:
LOW DC BUS VOLTAGE
DC Bus Voltage Imbalance (Software) Fault
The 1/2 DC bus voltage magnitude must remain within
+/- 100 Vdc of the total DC bus voltage divided by two.
If the 1/2 DC bus magnitude exceeds the +/- 100 Vdc
tolerances, the unit will fault and immediately shut down.
This safety will lock out on the 1st fault. The fault will
be a unit fault. Below is the Status display fault message:
UNIT FAULT:
DC BUS VOLTAGE IMBALANCE
High Motor Current (Hardware) Fault
The three output lines to each phase of the compressor
motor are monitored via three current transformers
within the VSD. The unit’s three phases of instantaneous
output current will be compared to a predetermined limit,
which is contained in hardware.
The nominal peak current trip level is 649.5 Amps (626
A min. / 674 A max.). The variation in trip point is the
result of component tolerances on the VSD Logic Board.
If the peak current limit is exceeded, the unit will fault
and shutdown immediately.
This fault is an auto-restart safety that will lock out
system on the 3rd fault in 90 minutes. The fault will be
an individual system/compressor fault. Following is a
sample Status display fault message:
SYS X FAULT: HIGH MOTOR CURRENT
X indicates the system and FAULT indicates the system is
in a “FAULT” condition and will restart or “LOCKOUT”
and will not restart until the operator clears the fault
using the keypad.