LW’s What is it?
Gas Fired Furnaces
1
What is this?
2
This is a combination
fan-high limit thermostat
The three set point
markers are for:
High Limit
Fan On
Fan Off
3
What is this?
4
Blower and Motor Assembly
This motor is
secured to the
blower housing
using a clamp
around bell band
type mounting
bracket.
This motor has
three wires.
It is a two
speed motor.
These rubber
grommets reduce
the vibration
transmitted from the
blower wheel motor
assembly to the
blower housing.
These two purple
wires connect to
the run capacitor.
5
What is this?
6
This is a run capacitor
While it can be tested
with a capacitor most
technicians test it
with their ohmmeter.
The letters 5uf indicate
that this capacitor has a
capacity of 5 microfarads.
A replacement should
have the same capacity
or within +/- 5%.
This capacitor has a
voltage rating of
370 VAC.
A replacement capacitor
should have the same
or higher voltage rating.
7
What is this?
8
This is the high voltage igniter
terminal on the Igniter Module
This terminal may
have as much as
15,000 volts on it.
Do not touch it.
The spark igniter
cable connects to
this terminal
and runs to the
spark igniter.
9
What is this?
What does the
G terminal
connect to?
What does the
Y terminal
connect to?
What does the
R terminal
connect to?
What does the
W terminal
connect to?
10
This is the low voltage (24) terminal strip
on the furnace solid state board
The G terminal
passes power to the
indoor fan relay coil.
The Y terminal
connects to the
thermostat and the
compressor contactor.
The R terminal
brings power from
one side of the
transformer to the
board and then to
the thermostat.
The W terminal
brings power from
the thermostat to the
heating controls
on the board.
11
What is this?
12
This is the induced draft
pressure switch
Upon a call for heat the first thing that starts is the
induced draft blower motor. When the blower
develops sufficient pressure the pressure switch
closes and passes power to the heating controls.
This pressure switch is normally open.
It is not field repairable and cannot be adjusted.
13
What is this?
14
This is the
induced draft blower assembly
This is the
induced
draft blower
housing.
This motor
has a sleeve
bearing that
cannot be
oiled.
This is the induced draft blower motor.
15
What is this?
16
This is a combination gas valve
This is the manual control knob
This
is the
gas inlet
connection
This is the
gas outlet
connection
17
What is this?
18
This is a flame roll out switch
This switch is normally
closed. If it senses the
presence of a flame it
will open the circuit.
It is a manual reset
safety device.
The red reset button
must be manually
depressed for the
switch to close.
This switch is set to
open the circuit when
it senses a temperature
of 210 degrees F.
As this is a safety
device it can not be
jumped out to allow
the furnace to operate.
19
What is this?
20
This is a Molex brand
pin and sleeve connector
To remove the
white half of the
connector from
the board
these two clips,
one on each side,
must be pressed
and the connector
pulled straight out.
Multimeter test
lead probes can
be slipped
down any of
these holes to
make contact
with the wires.
This connector is “indexed”.
That is it can not be installed incorrectly.
It will mate with the black half only one way.
21
What is this?
22
This is the dust cap for the gas
pressure regulator on a gas valve
To adjust the gas
pressure to the burner
remove the dust cover
and under it will be
a screw.
Turn it CCW to increase
the gas pressure.
Turn it CW to decrease
the gas pressure.
23
What is this?
24
This is a
control circuit transformer
The black
and
white wires
connect to
the primary
of the
transformer,
that is the
120 volt
supply
source.
The blue and yellow wires connect to the secondary, the 24 volt,
side of the transformer. One wire will connect to the R terminal
on the solid state board and the other wire will connect to the
common terminal on the solid state board.
25
What is this?
26
This is the heat exchanger
in a gas furnace
For any furnace over
five years old it is
recommended that it
be checked at the
beginning of each
heating season for
possible cracks.
The best way to check a
heat exchanger for cracks is to
use a carbon monoxide meter
like this one.
27
What is this?
28
This is a
pilot and igniter assembly
These create the spark
and detect the presence
of the pilot flame.
This is the pilot.
29
What is this?
30
This is the burner compartment
of a down flow gas furnace
Can you identify at least ten components in this picture?
31
What is this?
32
This is a solid state printed
circuit board for a gas furnace
This small
LED
is very
important
as it can tell
you what the
status of the
system is.
By knowing the LED fault code
you can troubleshoot the furnace.
This is where the wires from the
thermostat and the condensing
unit connect.
33
What is this?
34
This is a point to point electrical
diagram for a gas furnace
35
What is this?
36
This is a solid state board
for a gas furnace
This board has the LED fault codes listed on the face of the board.
37
This is a solid state board
for a gas furnace
This fuse protects the board from short circuits.
These are four DIP switches. They set the amount of delay on the flow motor.
38
What is this?
39
This is another solid state board
for a gas furnace
Do you see things that this board and the previous board have in common?
40
What is this?
41
This is a
Heating & Cooling Thermostat
When the system has a
transformer for the
heating system the red
wire from the transformer
is connected to the
RH terminal.
This is where you set
the heat anticipator.
When the system has a
transformer for the
cooling system the red
wire from the transformer
connects to the
RC terminal.
When the system has
only one transformer the
red wire connects to
either the RH or RC and
a jumper is run between
the RH & RC terminals.
This is where you set the point level.
42
What is this?
43
This is the blower compartment of an
up-flow Lennox brand furnace
44
What does this do?
45
What does this do?
This is the blower
door safety switch.
When this safety
switch is open the
furnace will not
operate and the
blower will not run.
Should the furnace operate with the blower
door removed it is possible that products of
combustion could be circulated into the
living spaces and people could be made sick
or even killed. It must never be defeated
except when troubleshooting the furnace.
46
What is this?
47
This is a burner
This
is a gas jet
or orifice.
Each orifice must be sized for the capacity of the
furnace and the number of burners. Different fuels such
as natural gas or butane require different sizes of
orifices for the same heating capacity.
48
What is this?
49
This is the
control circuit transformer
50
What is this?
How many components can you identify?
51
This is the burner compartment
J-Box, High Limit Switch, Flame Sensor, Roll Out Switch,
Gas Valve, Manifold Burner, Molex Connector
52
What is this?
53
This is a high limit switch
This is a limit
switch that is set
to open at 180
degrees F. and
close at 160 F.
(180-20=160).
This limit will
automatically
reset when it
cools down below
160 degrees F.
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The End
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