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 motor 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 collector outputs of the Microprocessor Board energize the DC relays or triacs by pulling the other side of the relay coil/triac 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 System 1 for control system circuitry servicing: specifically, the 115VAC feed to Relay Output Board 1 which energizes contactors, solenoids, and system #1 compressor heater.

CB2 allows removal of control power from System 2 for control system circuitry servicing: specifically, the 115VAC feed to Relay Output Board 2 which energizes contactors, solenoids, and system #2 compressor heater.

CB3 allows removal of control power to the Mi- croprocessor Board, Power Supply Board, I/O Expansion 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.

FORM 201.19-NM1 (204)

REMOVING 115VAC power to CB3 or opening CB3 removes power from the evaporator heaters. This could cause evaporator freeze-up in low ambient temperatures. Removing power from or opening CB1 or CB2 removes power from the respective compressor heater and should be avoided.

1.8 TRANSFORMERS

3 Transformers (2T, 3T, and 4T) are located in the Control Panel. These transformers convert the 115VAC Control Power Input to 24VAC to operate the micropro- cessor circuitry.

2T: This 75VA transformer supplies the 24VAC to the power supply board.

3T: Supplies the I/O Expansion Board # 1 voltage for slide valve control.

4T: Supplies 24VAC power to the 2ACE Motor Protector Modules.

1.9 MOTOR PROTECTION MODULES

A Motor Protection Module for each compressor is lo- cated in the Control Panel. These modules supply motor over-temperature protection, 3-phase current protection, phase imbalance, phase rotation, and a 7 segment display for use when programming or troubleshooting.

The motor over-temperature protection is supplied by 3 temperature sensors imbedded in the motor windings 120 degrees apart. The module monitors these sensors, allowing it to sense a hot winding and shut down the compressor if motor cooling is inadequate.

The on-board C.T.s provide 3-phase current protection. The C.T.s look at current on each phase of power to the motor and send an analog signal proportional to aver- age motor current to the I/O Expansion board and on to the microprocessor board for microprocessor low/high current protection and current display. This allows the micro to monitor current and shut a system down if low or high motor current is sensed. This is a non-adjustable protection circuit electronically sized to a system's mo- tor specifications.

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