I-Unit Components - Lennox LGT Series Unit Information

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 disconnect
switch(es). Unit may have multiple power
supplies.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic
electronic components. Take precautions
to neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
All 7.5 through 12.5 ton (38.1 through 70.3 kW) units are
configure to order units (CTO). The LGT unit components
are shown in figure 1. All units come standard with 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
LGT control box components are shown in figure 2. The
control box is located in the upper portion of the compres-
sor 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 T43 (Re-Heat Units)
T43 is a single line voltage to 24VAC and ties into T1.
See unit diagram. T43 is mounted in the control box. The
transformer supplies power to control circuits (through
T1).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 transformers use a
single primary voltage tap.
3-Control Transformer T1
All use a single line voltage to 24VAC transformer mount-
ed in the control box. Transformer supplies power to con-
trol circuits in the unit. The transformer is rated at 92VA
and is protected by a 6 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) volt-
age transformers use a single primary voltage tap.
discharge can affect
208/230V TRANSFORMER
ORANGE
4-Outdoor Fan Relay K10, K68
Outdoor fan relays K10 and K68 are DPDT relays with a
24VAC coil. In standard and high efficiency units, K10 and
K68 energize condenser fans B4 and B5.
5-Outdoor Fan Capacitors C1, C2
Fan capacitors C1 and C2 are used to assist in the start
up of condenser fans B4 and B5. Capacitor size varies
with unit tonnage and voltage.
LGT092-102 all voltages - 370V/10 MFD
LGT120-150 J volt - 370/10 MFD
LGT120-150 G volt - 370V/12.5 MFD
LGT120-150 Y volt - 370V/15 MFD
6-C. A. I. Transformers T3 575V Units
All LGT 575 (J) voltage units use transformer T3. The auto
voltage to 230VAC transformer is mounted in the control
box. The transformer has an output rating of 0.5A. T3
transformer supplies 230 VAC power to combustion air
blower motor (B6).
7-Compressor Contactor K1, K2
All compressor contactors are three-pole, double-break
contactors with 24VAC coils. K1 and K2 (both energized
by A55) energize compressors B1 and B2.
8-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
system if ignition is not obtained after the third trial. Reset
after lockout requires only breaking and remaking thermo-
stat 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 se-
quence and continue until flame is established or system
locks out. For a more detailed description see the Gas
Heat Components section.
9-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 LGT units equipped with
the optional power exhaust dampers. K65 is energized by
the economizer control panel (A56), after the economizer
dampers reach 50% open (adjustable in CORE). When
K65 closes, the exhaust fan B10 is are energized.
Page 14
BLUE YELLOW
SECONDARY
208 VOLTS
RED
230 VOLTS
PRIMARY
BLACK
FIGURE 3