JOHNSON CONTROLS
236
FORM 201.23-NM2
ISSUE DATE: 3/9/2015
SECTION 8 - MICROPANEL
Immediate Fault shutdowns are often accompanied
by audible motor backspin due to equalizing of the
differential between discharge and suction when the
compressor is turned off while rotating at high speeds.
This should not cause concern and will not damage the
chiller.
Each fault outlined in the descriptions that follow will
indicate whether it is a hardware or software generated
fault.
It will be noted the “ramped” shutdown results in mini-
mal compressor backspin and noise associated with
backspin. “Immediate” shutdowns will result in com-
pressor backspin and a higher noise level based upon
the differential pressure between discharge and suction.
When a VSD fault occurs, the VSD Logic Board cap-
tures VSD data in the onboard battery backed RAM.
At the same time, the VSD Board “Fault Relay” will
open, signaling the Chiller Control Board micropro-
cessor to save a snapshot of system data. The VSD
Logic Board then transmits the fault data to the Chill-
er Control Board microprocessor on the next comms
between the two boards. If the Chiller Control Board
receives the comms fault indication before the Fault
Relay signal, it will immediately save a snapshot of
system data when the comms fault is recognized. This
also enables the microprocessor to capture fault data
if the Fault relay fails. Both the system and VSD fault
data are then stored in the Chiller Control Board his-
tory buffers. Any additional faults that may occur dur-
ing shutdown on the first fault or between the first fault
and the next comms will also be stored and transmit-
ted to the Chiller Control Board along with the original
fault data. This data will be stored as “ALL FAULT”
data.
When the control panel acknowledges a fault (via the
fault acknowledge bit in comms) the fault relay will be
reset (closed) by the VSD Logic Board and the fault
indication flag (in comms) will be reset.
The fault relay will not open when a non-running fault
occurs. In this case, the system will be inhibited from
running until the fault condition is corrected. An inhibit
message will be displayed on the panel display indi-
cating the system is not allowed to run. Examples of
this type of fault would be the High Internal Ambient
fault and the VSD CT Plug Fault. When the chiller re-
ceives the transmitted fault data via comms, it will save
a snapshot of system data in the history buffer even
though the chiller is not running.
Some faults will be unit faults; other faults will be sys-
tem (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 per-
mitted to start.
Pre-charge Low DC Bus Voltage (Software) Fault
The DC Bus voltage must reach at least 50VDC within
four seconds and 500VDC 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 un-
til the operator clears the fault using the keypad.
Summary of Contents for YCIV0157
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