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VIII-Belt Drive Supply Air Inverter
The supply air inverter or variable frequency drive (VFD), is
located in the compressor compartment. The VFD stages the
amount of supply airflow according to the number of com
pressors operating.
The amount of airflow for each stage is set in the Unit Con
troller when the unit is initially commissioned. Each value is
recorded on a label on the inside of the compressor access
panel. Settings can also be read on the Unit Controller dis
play. Use one of the following menus.
M2 Unit Controllers:
Data > Status > Blower
M3 Unit Controllers:
DATA > ADVANCED STATUS > BLOWER > BLOWER
STATUS
Use figure 50 to determine whether the VFD should be pro
viding a staged output to the blower motor.
WARNING
ELECTRICAL SHOCK HAZARD.
Failure to follow instructions exactly could result in
serious injury or death.
VFD HOLDS A POTENTIALLY LETHAL CHARGE UP
TO 10 MINUTES AFTER POWER HAS BEEN
DISCONNECTED. Do not open VFD cover until 10
minutes AFTER power source has been
disconnected and power lamp has turned off.
Read manual provided by VFD manufacturer.
Carefully review and follow all safety warnings in that
manual also.
INPUTS REQUIRED TO STAGE SUPPLY AIR BLOWER
0-10VDC signal from the Unit Controller is
used to vary the supply air blower stage.
This signal is polarity sensitive - if supply
air flow is not staging, reverse leads.
M2 Unit Controller
The Unit Controller (A55) energizes K203
relay coil. N.O. K203-2 closes to enable
supply air blower forward rotation.
24VAC required
to operate the
inverter.
See 537407-01.
M3 Unit Controller
See 537616-02.
VFD feedback circuit; a
VFD fault condition will
open N.C. contacts, shut
down the VFD, and the
Unit Controller will display
an alarm.
FIGURE 50
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