Scholar V VAIVA Maintenance & Service Manual 10/2017 Rev.2
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The driver board conditions the power going to the compressor to allow speed control and
capacity variation.
A 24 VAC run signal comes from the PLC to tell the compressor to operate. A 4-20 milliamp
analog signal comes from the PLC to set the correct speed. Since the driver board requires a
DC voltage for the speed signal, the milliamp signal is converted to a voltage signal with a 500
ohm resistor. It is important that this resistor is in the system and securely connected.
Compressor Driver Board
The driver board conditions the power going to the compressor to allow speed control
and capacity variation.
A 24 VAC run signal comes from the PLC to tell the compressor to operate. A 4-20
milliamp analog signal comes from the PLC to set the correct speed. Since the driver
board requires a DC voltage for the speed signal, the milliamp signal is converted to a
voltage signal with a 500 ohm resistor. It is important that this resistor is in the system
and securely connected.
24 VAC run signal connected
to LO and C
4-20 milliamp speed control
signal from PLC. Converted
to DC voltage with 500 ohm
resistor
Power to Compressor
Power Input from High
Voltage Inductors
Figure 16. PLC Compressor Driver Board
Indoor Blower Controller
Control Cable
to Indoor Blower
0-10 VDC speed signal from
PLC. Already converted to
DC with resistor on PLC
24 VAC run signal
from PLC
Figure 17. Indoor Blower Controller
