1.6 Circuit Breakers; Current Transformers (C.t.); Transformers - York MILLENIUM YCAS Series Installation Operation & Maintenance

Micro Panel Contents
I/O Expansion Board
The I/O Expansion Board provides multiplexing to al-
low additional inputs to be connected to the Micropro-
cessor Board via a single data line. The additional in-
puts are multiplexed according to the selection made
by the Microprocessor through address lines.
Signals routed through the I/O Expansion Board include
Discharge Temperature, Current Transformer outputs
(motor current signals), and Oil Temperature.
Included on the I/O Expansion Board are the outputs for
the slide valve control. This control consists of a Digital
to Analog Converter (DAC) and power transistors to
modulate current through the slide valve solenoids.
Relay Output Boards
One Relay Output Board per system operates the mo-
tor contactors/starters, solenoid valves, and heaters
which control system operation.
The relay boards are located in the logic section of the
control panel(s). The boards convert 0 - 12VDC logic
levels outputs from the Microprocessor Board to
115VAC levels used by the contactors, valves, etc.
The common side of all relays on the Relay Output
Board is connected to +12VDC REG. The open collec-
tor outputs of the Microprocessor Board energize the
DC relays or triacs by pulling the other side of the relay
coil to 0VDC. When not energized, both sides of the
relay coils or triacs will be at +12VDC potential.

1.6 CIRCUIT BREAKERS

Three Circuit Breakers are provided for the 115VAC
controls.
• CB1 allows removal of control power from respec-
tive System 1 for control system circuitry servicing.
Specifically, the 115VAC feed to Relay Output Board
1 which energizes contactors and solenoids.
• CB2 allows removal of control power from respec-
tive System 2 for control system circuitry servicing.
Specifically, the 115VAC feed to Relay Output
Board 2 which energizes contactors and solenoids.
100
• CB3 allows removal of control power to the Micro-
processor Board, Power Supply Board, I/O Expan-
sion Board, and Evaporator Heater.
The Circuit Breakers remove 115VAC
control power only. High voltage cir-
cuitry will still be energized from the
high voltage supply.
REMOVING 115VAC power to CB3
or opening CB3 removes power from
the evaporator heaters. This could
cause evaporator freeze-up in low am-
bient temperatures.

1.7 CURRENT TRANSFORMERS (C.T.)

C.T.s located internally in the Motor Protection Modules
on each of the 3 phases of the power wiring of each
compressor motor send AC signals proportional to motor
current to the Power Supply Board which rectifies and
filters the signals to variable DC Voltage (analog). These
analog levels are then fed to the Microprocessor Board
via the I/O Expansion Board allowing the microproces-
sor to monitor motor currents for low current, high cur-
rent, unbalanced current, and single phasing.
1.8

TRANSFORMERS

3 Transformers (2T, 3T, and 4T) are located in the Con-
trol Panel. These transformers convert the 115VAC
Control Power Input to 24VAC to operate the micro-
processor circuitry.
2T: This 75VA transformer supplies the 24VAC
microprocessor power supply.
3T: Supplies the I/O Expansion Board # 1 voltage for
slide valve control.
4T: Supplies power to the Motor Protector Modules.
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