Indirect Gas-Fired Heat Modules
5
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 of
them 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.
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
field-installed 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 extra stages.
1092 Control System
Used on 2:1 electronic modulating controls
.
The A1092
control system consists of an amplifier, a remote
temperature dial and a remote temperature sensor.
The amplifier and remote temperature dial are factory-
installed on the vest plate while the remote temperature
sensor must be field-installed. The temperature dial and
amplifier are installed in the furnace control center. Field
adjustments include discharge air temperature, which is
done by means of the Remote Temperature Dial.
Amplifier
Remote
Temperature Dial
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 only in the unit 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 located in the main unit control
center or the furnace control center
depending on the control type.
Input Converter
The input converter takes
an analog signal from a
microprocessor or a BMS
and converts it to a control
signal that can be used
by the FX programmable
controller. It is found in the
furnace control center.
FX Programmable Controller
Used on all 4:1 electronic
modulating controls and
8:1 staged turndown.
The FX controller turns on and
electronically modulates gas
valves. It will also enable the
ignition module. The FX controller has a digital readout
and four push buttons, one for Function, one for Enter
and two for scrolling up or down. It is pre-programmed
at the factory for each specific furnace configuration
and it may be used to control two 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.
Burner Manifold
Single Section
Burner Manifold
Split Burner
Manifold
S350 Controller
A350 Controller
®
