30
temperature, shut off the power to the furnace,
and replace the supply air limit switch.
DESCRIPTION OF COMPONENTS
Figure 26 shows the location of each of the
functional components described below. If any
component of the furnace must be replaced,
use only factory authorized replacement parts.
See the Replacement Parts List for each com-
ponent.
Flame Sensor –
The fl ame sensor acts to prove
that fl ame has carried over from the igniter to the
opposite end burner. If no fl ame is sensed, the
furnace will be shut down automatically.
Primary Gas Valve –
The gas valve controls the
fl ow of gas to all of the burners. When the gas
valve is energized it automatically opens and
regulates the gas pressure in the manifold.
Secondary Gas Valve –
The gas valve controls
the fl ow of gas to the high fi re burners only.
Pressure Switch –
The pressure switch verifi es
that the inducer is drawing the combustion gases
through the heat exchanger. It also senses a
blocked condensate drain condition.
Vent Pressure Switch –
The vent pressure
switch reacts to blockage in the vent or combus-
tion air piping.
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 fl ue gas
temperature increases above 160°F. This switch
protects the plastic fl ue system and the inducer
from over-temperature conditions.
Flame Roll-Out Switch –
This switch provides
fl ame roll-out protection to the furnace and
combustion air inlet pipe.
MAINTENANCE
It is recommended that the furnace be checked
yearly. At a minimum, this check should include
the following items.
Figure 24. Blower Speed Tap Location
R C Y G W
Flame Signal
Light (Yellow)
3 Amp Fuse
COM
24 V
HUM
Neutrals
4
1
5
2
6
3
4
1
5
2
6
3
1
2
3
7
8
9
4
5
6
1
2
3
EAC
HUM
M1
M2
M3
HEAT
COOL
L1
XFMR
Unused Motor
Leads
EAC
Electronic Air Tap
(.5A@ 120 VAC)
Status
Light (Red)
Humidifier Tap
(.5A@ 120 VAC)
Connect
Neutral
Lead of
Electronic
Air Cleaner
and/or Humidifier
Here.
Common
Leads
These motor speed taps are
not used for two-stage models
Y2
Y2
W2
Optional
Connector
Timing Switch
ADD-ON BOARD
Main Board
120 VAC
