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SECTION 7 – UNIT CONTROLS
The on-board power supply converts 24VAC from
75VA, 120/24 VAC 50/60Hz UL listed class 2 power
transformer to +12V, +5V and +3.3V using switching
and linear voltage regulators located on the I/O and
IPU II boards. These voltages are used to operate
integrated circuitry on the board. The 40 character
display and unit sensors (transducers and temperature
sensors) are supplied power for the microprocessor
board +5V supply. 24VAC is rectified, but not regulated,
to provide unregulated +30 VDC to supply all of the
digital inputs.
The IPU II board contains one green "Power" LED
to indicate that the board is powered up and one red
"Status" LED to indicate, by blinking, that the processor
is operating.
The I/O board contains one green "Power" LED to
indicate that the board is powered up and one red
"Status" LED to indicate by blinking that the processor
is operating. The I/O board also contains two sets of
Receiver/Transmit LED's, one for each available serial
communication port. The receive LED's are green, and
the Transmit LED's are red.
A jumper on the I/O board selects 4-20mA or 0-10
VDC as the input type on the remote temperature reset
analog input.
Unit Switch
A unit ON/OFF switch is located below the keypad.
This switch allows the operator to turn the entire unit
"OFF" if desired. The switch must be placed in the "ON"
position in order for the chiller to operate.
Display
The 40 character liquid crystal display (2 lines of 20
characters) is used for displaying system parameters
and operator messages.
The display in conjunction with the keypad, allows the
operator to view system operating parameters as well
as access programmed information already in memory.
The display has a lighted background for night viewing
and for viewing in direct sunlight.
When a key is pressed, such as the OPER DATA key,
system parameters will be displayed and will remain
on the display until another key is pressed. The system
parameters can be scrolled with the use of the ↑ (UP)
and ↓ (DOWN) arrow keys. The display will update all
information at a rate of about 1 per second.
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Display messages may show characters indicating
"greater than" (>) or "less than" (<). These characters
indicate the actual values are greater than or less than
the limit values which are being displayed.
Keypad
The 12 button non-tactile keypad allows the user
to retrieve vitals system parameters such as system
pressures, temperatures, compressor running times
and starts, option information on the chiller, and
system setpoints. This data is useful for monitoring
chiller operation, diagnosing potential problems,
troubleshooting, and commissioning the chiller.
It is essential the user become familiar with using the
keypad and display. This will allow the user to make full
use of the capabilities and diagnostic features available.
Battery Back-up
The IPU II contains a Real Time Clock integrated circuit
chip with an internal battery backup. The purpose of
this battery backup is to assure any programmed values
(setpoints, clock, cutouts, etc.) are not lost during a
power failure regardless of the time involved in a power
cut or shutdown period.
Transformer
A 75VA, 120/24VAC 50/60Hz transformer is provided
to supply power to the Microprocessor Board, which in
turn rectifies, filters, and regulates as necessary to supply
power to the display, sensors, and transducers.
Programming # of Compressors
The total number of compressors is programmable under
the Program Key. Dual (two) system chillers can have
4, 5, or 6 compressors.
FORM 150.72-NM3 (1020)
ISSUE DATE 10/05/2020
JOHNSON CONTROLS
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Troubleshooting
