Viii-Belt Drive Supply Air Inverter - Lennox LGH094U Unit Information

VIII-Belt Drive Supply Air Inverter

NOTE - Units equipped a Variable Frequency Drive (VFD)
are designed to operate on balanced, three-phase power.
Operating units on unbalanced three-phase power will re­
duce the reliability of all electrical components in the unit.
Unbalanced power is a result of the power delivery system
supplied by the local utility company. Factory-installed in­
verters are sized to drive blower motors with an equivalent
current rating using balanced three-phase power. If unbal­
anced three-phase power is supplied; the installer must re­
place the existing factory-installed inverter with an inverter
that has a higher current rating to allow for the imbalance.
Refer to the installation instructions for additional informa­
tion and available replacements.
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.
INPUTS REQUIRED TO STAGE SUPPLY AIR BLOWER
M2 Unit Controller
24VAC required
to operate the
inverter.
See 537407-01.
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.
The Unit Controller (A55) energizes K203
relay coil. N.O. K203-2 closes to enable
supply air blower forward rotation.
FIGURE 50
Page 67
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
disconnected and power lamp has turned off.
Read manual provided by VFD manufacturer.
Carefully review and follow all safety warnings in that
manual also.
M3 Unit Controller
See 537616-02.
source has been
VFD feedback circuit; a
VFD fault condition will
open N.C. contacts, shut
down the VFD, and the
Unit Controller will display
an alarm.