I-Unit Components - Lennox LGM Series Manual

I-UNIT COMPONENTS

WARNING
Electric shock hazard. Can cause injury
or death. Before attempting to perform
any service or maintenance, turn the
electrical power to unit OFF at discon­
nect switch(es). Unit may have multiple
power supplies.
All 7.5 through 12.5 ton units are configure to order units
(CTO). The LGM unit components are shown in figure 1 All
units come standard with1 hinged unit panels. All L1, L2
and L3 wiring is color coded; L1 is red, L2 is yellow and L3 is
blue.
A-Control Box Components
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can affect electronic com­
ponents. Take precautions during unit installation
and service to protect the unit's electronic con­
trols. Precautions will help to avoid control expo­
sure to electrostatic discharge by putting the unit,
the control and the technician at the same electro­
static potential. Neutralize electrostatic charge by
touching hand and all tools on an unpainted unit
surface, such as the gas valve or blower deck, be­
fore performing any service procedure.
LGM control box components are shown in figure 2. The
control box is located in the upper portion of the compressor
compartment.
1-Disconnect Switch S48 (Optional)
All units may be equipped with an optional disconnect
switch S48. Other factory or field installed optional circuit
breakers may be used, such as CB10. S48 and CB10 are
toggle switches, which can be used by the service techni­
cian to disconnect power to the unit.
2-Control Transformer T1
All use a single line voltage to 24VAC transformer mounted
in the control box. Transformer supplies power to control
circuits in the unit. The transformer is rated at 70VA and is
protected by a 3.5 amp circuit breaker (CB8). The 208/230
(Y) voltage transformers use primary voltage taps as
shown in figure 3, while 460 (G) and 575 (J) voltage trans­
formers use a single primary voltage tap.
208/230V TRANSFORMER
ORANGE
3-C. A. I. Transformers T3 all 575V units
All LGM (J) voltage units use transformer T3. The auto volt­
age to 230VAC transformer is mounted in the control box
behind the hinged panel to the right of the A192 Inverter for
Compressor Circuit 1. See Figure 2 The transformer has an
output rating of 0.5A. T3 transformer supplies 230 VAC
power to combustion air blower motor (B6).
4-Compressor Contactor K1, K2
All compressor contactors are three‐pole, double‐break
contactors with 24VAC coils. K1 and K2 (both energized by
A55) energize the A192 Inverter for compressor B1 and the
B2.
5-Burner Controls A3
A3 controls gas heat section burner controls. Burner con­
trols are factory set and are not adjustable. The control
makes three attempts at ignition and then locks out the sys­
tem if ignition is not obtained after the third trial. Reset after
lockout requires only breaking and remaking thermostat
demand. The control shuts off gas flow immediately in the
event of a gas or power failure. Upon restoration of gas and
power, the control will restart the ignition sequence and
continue until flame is established or system locks out. For
a more detailed description see the Gas Heat Components
section.
6-Power Exhaust Relay K65 (PED units)
Power exhaust relay K65 is a N.O. DPDT relay with a
24VAC coil. K65 is used in all LGM units equipped with the
optional power exhaust dampers. K65 is energized by the
unit controller A55, after the economizer dampers reach
50% open (adjustable in CORE APP). When K65 closes,
the exhaust fans B10 IS energized.
7-Unit Controller A55
The Unit Controller provides all unit control functions, unit
status information, unit diagnostics, programmable param­
eters and USB verification and profile sharing. Refer to the
Unit Controller guide provided with the unit. Thermostat
wires are connected to J297 on the Unit Controller.
8-Terminal Block TB13
TB13 terminal block distributes line voltage power to the
line voltage items in the unit.
Page 13
BLUE YELLOW
SECONDARY
208 VOLTS
RED
230 VOLTS
PRIMARY
BLACK
FIGURE 3