Dunham-Bush ACDX, Installation, Operation And Maintenance Instructions

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FIELD CONTROL WIRING (cont'd)
is set for the unit to operate. However, especially 5) Remote Chiller - On AUDX units with remote
in cases of low ambient temperature, the contacts chiller, field wiring is required for liquid line
should not be the sole means of controlling pump solenoids, load limit option thermostat, and water
operation. temperature sensors. The 120VAC wiring should
be run in a separate conduit from the sensor
wiring. Also, shielded cable must be used for the
sensor wiring with the shield grounded only to the
main unit sub-panel.
STAR-DELTA STARTING
OPEN TRANSITION (OPTIONAL)
Typical For All Compressors (Normally Open) auxiliary contacts close locking 1M1
On call for cooling, the controller contacts close, in the energized position. The compressor operates
energizing transition contactor (1C) and the five in the "Star" mode until 10TR transition timer times out
second transition timer (10TR). Transition contactor (five seconds) at which time contacts N.C. open and
(1C) power contacts close, tying the center legs of the de-energize (1C). Start contactor (1C) N.C. auxiliary
compressor motor windings together into "Star" contacts close, (10TR) timer N.O. contacts close,
(WYE) configuration. At the same time (1C-1) N.C. energizing compressor contactor, (1M2) power
(Normally Closed) auxiliary contacts open preventing contacts close, thereby completing the "Delta" wiring
(1M-2) from closing. (1C-2) N.O. (Normally Open) configuration. Compressor contactor (1M2) N.C.
auxiliary contacts then close, energizing contactor auxiliary contacts open, preventing (1C) star contactor
(1M1). The 1M1 power contacts close, applying from energizing until the next starting sequence.
power to the compressor winding. (1M1) N.O.
MICROCOMPUTER CONTROLLER
1. General Description The software for the computer is stored in three
Your Dunham-Bush ACDX/AUDX is controlled by EPROM chips (Electrically Programmable Read Only
an NC25 microcomputer system. The computer Memory) store general operating procedures
system is composed of a main microcomputer (algorithms) and is the same for all packages. The
board, several types of input/output (I/O) boards, EAROM chip (Electrically Alterable Read Only
and sensors. The I/O boards are connected to the Memory) stores the program that defines the logic for
microcomputer by ribbon cables. These hardware a particular unit. This software is called the data base.
components are controlled by the software Both of these chips retain their content when power is
program in the microcomputer. The software removed. The third type of memory is battery backed
determines the state of the output relays based RAM (Random Access Memory) and is used for
on the input values. temporary storage.
There are two types of inputs to the computer Information can be retrieved from the NC25 and
system. A digital input indicates whether or not displayed on a video display terminal. The RS232
voltage is present at the input. This could be used communications port is used. Refer to FORM 6372
to determine whether or not a contactor is pulled for more information.
in, a water flow switch is made, or the status of
other on/off devices. Another type of input is an
2. Microcomputer Hardware Precautions
analog input. An analog value is one that varies
continuously, such as temperature, pressure,
The following precautions must be taken while
current, etc. An analog input must be converted to working with the microcomputer system.
a digital value with an analog to digital (A/D)
converter board before the computer can process
2.1. Do not lay the solder side of a computer board
the data. on a metallic surface. This may damage the
The computer system outputs are relays that
switch the 115 VAC control devices such as
2.2. Cover the computer components completely
contactors and solenoids. when drilling sheet metal near the computer.
different types of computer memory chips. The two
battery on the board.
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