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29
Verifying Operation of the Supply
Air Limit Switch
To verify operation of the supply air limit
switch, make sure that the blower door is in
place and that there is power to the furnace.
Completely block the return airflow to the fur-
nace by installing a close-off plate in place of or
upstream of the filter(s). Set the thermostat
above room temperature and verify that the
Sequence of Operation is as described in these
instructions. The supply air limit switch should
function to turn off the gas valve within approxi-
mately five minutes. The circulating air and
combustion blowers should continue to run
when the supply air limit switch opens. Remove
the close-off plate immediately after the supply
air limit switch opens. If the furnace operates
for more than five minutes with no return air, set
the thermostat below room temperature, shut
off the power to the furnace, and replace the
supply air limit switch.
DESCRIPTION OF COMPONENTS
Figure 28 shows the location of each of the
functional components described below. If
any component of the furnace must be re-
placed, use only factory authorized replace-
ment parts. See the Replacement Parts List
for each component.
R C Y G W
Flame Signal
Light (Yellow)
60
90
120
180
TWIN
3 Amp Fuse
COM
24 V
HUM
Neutrals
41
52
63
7
8
9
4
5
6
1
2
3
EAC
HUM
M1
M2
M3
COOL
HEAT
L1
XFMR
Unused Motor
Leads
EAC
Electronic Air Tap
(.5A@ 120 VAC)
Status
Light (Red)
Heating Speed Tap
Cooling
Speed Tap
Humidifier Tap
(.5A@ 120 VAC)
Connect
Neutral
Lead of
Electronic
Air Cleaner
and/or Humidifier
Here.
Common
Leads
Blower Off
Timing
Figure 25. Blower Speed Tap Location
Flame Sensor – The flame sensor acts to prove
that flame has carried over from the ignitor to the
opposite end burner. If no flame is sensed, the
furnace will be shut down automatically.
Gas Valve – The gas valve controls the flow of
gas to the burners. When the gas valve is
energized it automatically opens and regulates
the gas pressure in the manifold.
Pressure Switch – The pressure switch verifies
that the inducer is drawing the combustion gases
through the heat exchanger. It also senses a
blocked condensate drain condition.
Vent Pressure Switch (G6RD Only) – The vent
pressure switch reacts to blockage in the vent or
combustion air piping. It is utilized in G6RD
furnaces only.
Supply Air Limit Switch – The supply air limit
switch prevents the air temperature leaving the
furnace from exceeding the maximum outlet air
temperature.
Vent Safety Switch – The vent safety switch
shuts the furnace down if the outlet flue gas
temperature increases above 160°F. This switch
protects the plastic flue system and the inducer
from over-temperature conditions.
Flame Roll-Out Switch – This switch provides
flame roll-out protection to the furnace and
combustion air inlet pipe.