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SECTION 7 - OPERATION
sors to start and begin operation of the compressors.
The compressors speed will be ramped to the minimum
start frequency and increase speed as needed in an ef-
fort to regulate the leaving chilled liquid temperature to
meet the desired Setpoint. Unit Warnings
Unit warning
Unit warning operation
Unit warnings are caused when a condition is
present requiring operator intervention to restart the
unit. All setpoints, program values, and options should
be checked before operating the unit. Warnings are
not logged to the history buffer. If a unit warning is in
effect, the message will be displayed to the operator
when the STATUS key is pressed.
Low battery warning
The LOW BATTERY WARNING can only occur at
unit power-up. On micropanel power-up, the RTC
battery is checked to see if it is still operational. If
it is, normal unit operation is allowed. If the battery
voltage is determined to be low, the following warning
message is displayed indefinitely.
UNIT WARNING: !! LOW BATTERY !!
CHECK SETPOINTS/PROGRAM/OPTIONS/TIME
If a low battery condition exists, all programmed
setpoints, program values, time, schedule, and history
buffers will have been lost. These values will all be
reset to their default values, which may not be the
desired operating values. Once a bad battery is
detected, the unit will be prevented from running un-
til the MANUAL OVERRIDE key is pressed. Once
the MANUAL OVERRIDE key is pressed, the anti
recycle timers will be set to the programmed default anti
recycle time to allow the operator sufficient time to
check setpoints, program values, and so on.
If a low battery is detected, it should be replaced as
soon as possible. The programmed values will all be
lost and the unit will be prevented from running on the
next power interruption.
Microboard (331-03478-XXX)
The 331-03478-xxx microboard was developed as
a direct replacement for the 031-02478-xxx line of
microboards. No adapter harness is required when
replacing a 02478 with the new 03478. The 03478
uses the IPUII processor card and provides some new
features for the chillers that the 02478 did not have.
106
The 03478 program resides in flash memory instead
of EPROM. Program updates are accomplished by
loading the new program from an SD card inserted into
the SD card reader/writer. This same SD card reader/
writer also allows the user to datalog the operating
parameters to an SD card every 5 seconds. This infor-
mation is invaluable when troubleshooting unit and
system problems since it allows the service techni-
cian to view operating parameters before a unit fault.
Details on the new datalogging capability are explained
in the OPTIONS Key area of this manual. A Real Time
Clock/BRAM keeps time and setpoints during power
outages.
See
Figure 18 on page 102 to locate the following
ports of the 03478 microboard.
Power supplies and LEDs
The 03478 has LEDs to indicate various states of op-
eration of the microboard.
STATUS – Flashes every 1/2 second to indicate that
the base board processor is running its program.
POWER – On solid indicates that the base board +12
V and +5 V power supplies are operational.
TX1 – Red LED flashes when transmitting data out
Port 1 TB3 (Future native communications BAS port).
RX1 – Green LED flashes when receiving data in Port
1 TB3 (Future native communications BAS port).
TX2 – Red LED that flashes when transmitting data
out Port 2 (E-Link TB2 or printer TB1).
RX2 – Green LED that flashes when receiving data in
Port 2 (E-Link TB2 or printer TB1).
VSD_TX – Red LED that flashes when transmitting
data out Port 3 to the VSD Logic board.
VSD_RX – Green LED that flashes when receiving
data in Port 3 from the VSD Logic board.
24 VAC power is applied to the 331-03478-xxx
microboard connector J12 and is then used to create the
various DC power sources required by the microboard
circuitry. If the chiller control is malfunctioning, the
power supply test points should be measured to deter-
mine the status of the microboard.
Form 201.28-NM1.1
Issue date: 08/06/2021
JOHNSON CONTROLS
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