Typical Furnace, Electrical And Control Components - LG GEN2 Series Installation And Operation Manual

Typical Furnace, Electrical and Control Components

Microprocessor
The microprocessor
provides the call for heat
to the ignition controller
and also monitors the
discharge air temperature.
It is found in the unit's
main control center. On units with electronic modulation,
it also determines the required burner firing rate.
Discharge Air Temp Sensor
This sensor is shipped with all units
and must be field-installed in the
discharge air duct. This may be
shipped in the main unit control center
or in the furnace control center,
depending on the control type.
pCOe Expansion Board
Used on all 4:1 or high turndown
electronic modulating controls
when a microprocessor controller
is present in the unit.
The pCOe acts as an interface
between the furnace and
microprocessor controller. It
sends the signal to enable the
ignition controller, modulate the gas valve, speed up the
combustion fan, and it monitors the furnace for alarms.
The expansion board has no built-in logic since the main
microprocessor controller contains the built-in logic.
Furnace Controller
Used on all stand-alone 4:1 electronic
modulating controls and 8:1 staged controls.
The furnace controller provides
power to the gas valve(s) and
electronically adjusts the valve(s).
It will also enable the ignition
module. The furnace controller has
a digital readout and six push buttons: Enter, Alarm,
Program, Escape and arrows for Up or Down. It is pre-
programmed at the factory for each specific furnace
configuration and it may be used to control up to three
furnaces at the same time.
Ignition Controller
This controller is found only in
the furnace control center. It
has an LED indicator light on
the top right of the controller
that will flash GREEN for
normal operation or RED
for an error. Some furnace
configurations have two of these controllers.
Airflow Switch
Airflow switches are used on both
furnaces and are found on the furnace
vest plate. If the combustion blower
is multi-speed, there will be two
airflow switches and each will switch
in response to a different pressure.
The switch is connected to the combustion blower
by means of a vacuum tube and is used to sense
operation of the combustion blower. The internal switch
is Normally Open (NO). If the blower fails to operate, the
open circuit will cause the ignition controller to disable
the furnace.
Flame Igniter
The igniter receives a high voltage
input from the ignition controller to
produce a spark between the two
electrodes. It operates only during
the ignition phase. On split burner
manifolds, there will be two igniters.
Flame Sensor
The flame sensor is identical to the flame igniter. It is
located on the opposite end of the burner manifold from
the igniter. On split burner manifolds, there will be two
flame sensors.
Auto Reset High Temperature
Limit Switch
This limit switch is installed through the
vest plate into the supply air plenum.
A350 and S350 Control System
Used on two stage and
single stage controls.
Used in conjunction
with a discharge remote
temperature sensor. Has an
LED indicator light to show
when the output relay is
energized. When used with
multiple stages, the S350
controller is used for the
additional stages.
Burner Manifold
Single Section
Burner Manifold
A350 S350
Controller Controller