Furnace Control Center; Furnace Control Center Components; Typical Furnace Control Logic - LG GEN2 Series Installation And Operation Manual

Furnace Control Center

Each ventilating unit containing one or more furnaces will have a furnace control center located on the furnace vest
plate. The control center receives high voltage AC from the main unit control center and in most cases, also receives low
voltage control signals (call for heat) from the main unit control center. In all cases, see the unit-specific wiring schematic
located inside the furnace door.

Furnace Control Center Components

(Components and their locations will vary.)
Components shown are for a typical 4:1 turndown electronic modulation configuration.
12
9
3
14
4
5
6
11

Typical Furnace Control Logic

In all cases, refer to the unit-specific wiring diagram located on the unit control center door.
This illustration is only for a typical 4:1 turndown electronic modulation configuration.
Optional Microprocessor Controller Configuration
Microprocessor
Controller
Located in
unit main
control center
Expansion
Board
Activates
Ignition Controller
Ignition
Controller
Activates
Spark to Igniter
Combination Valve
13
2
7
8
1
10
Activates and modulates
Modulating Valve
Controls speed
of Combustion
Blower
Ignition
Controller
Activates
Combustion Blower
Activates
Combination Valve
High Voltage Side
1. Inducer Relay (controls combustion fan)
2. Combustion Blower
3. Power Transformer
Low Voltage Side
4. Ignition Controller (also has high voltage present)
5. Furnace Controller (modulates heat and switches
entire furnace on/off)
6. 24 volt Terminal Strip
Control Sensors
7. High Temperature Sensor (auto reset)
8. Airflow Switches
9. Flame Sensor
Gas Train
10. Combination Valve
11. Modulating Valve
12. Burner Manifold
13. Collector Box
14. Spark Rod
Temperature Sensor
If there is no Microprocessor
Controller, the sensor is connected
to the furnace Controller
Furnace
Controller
Activates and modulates
Modulating Valve
Controls speed
Activates
of Combustion
Ignition Controller
Blower
Activates
Combustion Blower
Spark to Igniter
1. Microprocessor with pCOe
(if present) or furnace
controller senses low
temperature from the
temperature sensor, then
sends an enable signal to
the ignition controller, and
0-10 VDC signal to the
modulating valve.
2. Ignition controller receives
call for heat from pCOe
expansion board or furnace
controller, sends spark
to igniter, and activates
the combination valve. It
looks for verification that
the combustion blower is
running.
3. Flame sensor detects flame
and the trial for ignition
ends.