Lennox LGM Series Manual page 17

1-Compressors B1, B2
Units are equipped with one variable speed scroll and one
fixed scroll compressor each operating on a separate cool­
ing circuit. Compressor capacity may vary from stage to
stage. In all cases, the capacity of each compressor is
added to reach the total capacity of the unit. See "SPECIFI­
CATIONS" and "ELECTRICAL DATA" (table of contents)
or compressor nameplate for compressor specifications.
WARNING
Electrical shock hazard. Compressor must be
grounded. Do not operate without protective cover
over terminals. Disconnect power before removing
protective cover. Discharge capacitors before ser­
vicing unit. Failure to follow these precautions could
cause electrical shock resulting in injury or death.
Each compressor is energized by a corresponding com­
pressor contactor, , however contactor (K1) provides pow­
er to the compressor inverter (A192) which then controls
compressor according to signal from unit controller (A55).
NOTE-Refer to the wiring diagram section for specific
unit operation.
If Interlink compressor replacement is necessary, call
1-800-453-6669.
IMPORTANT
Some scroll compressors have an internal vacuum
protector that will unload scrolls when suction pres­
sure goes below 20 psig. A hissing sound will be
heard when the compressor is running unloaded.
Protector will reset when low pressure in system
rises above 40 psig. DO NOT REPLACE COMPRES­
SOR.
2-Compressor Inverter A192
Electrical Hazard
High Voltage
Wait 7 Minutes
Electrical
charge. Do not remove this panel or ser­
vice this area for 7 minutes after the
power has been removed.
See figure 7 for compressor inverter controls located be­
hind the hinged control panel.
The inverter varies the compressor speed (capacity) by
converting an AC input signal to a pulse high voltage DC
output. To initiate cooling operation, the Unit Controller
(A55) supplies a control signal to the inverter (A192) via a
MODBUS protocol. Inverter status and diagnostics are
continuously monitored and reported to the Unit Controller
such as:
-Improper Unit Controller input voltage compared to unit
model number
-High input voltage
-Low input voltage
-Imbalanced input voltage
-A communication issue - check MODBUS communica-
tion wire for good connections between the Unit
Controller and the inverter board.
See table 5 for inverter-related alarms.
Inverter component wire routing is shown in figure 8.
Electrical shock hazard. Variable speed compressor
components must be grounded. Failure to follow
these precautions could cause electrical shock re­
sulting in injury or death.
Page 17
WARNING
components
WARNING
may hold