102
18-CE03D1-1F-EN
Sequence of Operation
N
No
otte
e:: The seven segment LED readout is based on
thermostat input. During a simultaneous call for
W1 and W2, the seven segment LED will read
“
Xt2
”, although the IFC will process the call for
1
st
stage heat first.
1
1
sstt
S
Stta
ag
ge
e G
Ga
ass H
He
ea
attiin
ng
g
1. R – W1 contacts close on the thermostat sending
24VAC to the W1 low voltage terminal of the IFC.
Technician should read 24VAC from W1 to B/C. The
seven segment LED will read “
Xt1
”.
2. T
Th
he
e IIF
FC
C p
pe
errffo
orrm
mss a
a sse
ellff--cch
he
ecckk rro
ou
uttiin
ne
e a
an
nd
d tth
he
en
n
cco
on
nffiirrm
mss::
a. Condensate pressure switch and Inducer limit
switch are closed by sending 24VAC out the
HLO terminal and monitoring the ILI input.
b. Flame roll-out switches (FRS) 1 & 2, main
thermal limit (TCO), and any reverse air flow
(RAF) switches are closed by sending 24VAC out
the HLO terminal and monitoring the HLI input.
N
No
otte
e:: Downflow units will have one reverse air
flow switch (RAF).
Upflow units will have two reverse air
flow switches (RAF).
c. Pressure switch 1 (PS1) and pressure switch 2
(PS2) are opened by sending 24VAC out the
HLO terminal, through the limit switches, and
monitoring the PS1 and PS2 inputs.
N
No
otte
e:: If a thermal limit is open, 24VAC will not
be present at either pressure switch.
3. After steps 2a, b, and c are confirmed, the variable
speed inducer is energized and will run at the
predetermined factory default 1
st
stage inducer
speed. As the inducer ramps up, PS1 will close.
4. When PS1 closes, the ignitor relay on the IFC will
close. The ignitor is energized and warm up is
approximately 20 seconds.
5. After the ignitor warm up, the 1
st
stage gas valve
relay is closed, energizing the 1
st
stage gas valve
solenoid to allow ignition.
6. The first burner will ignite and flame will crossover
to the remaining burners, establishing current to
the flame sensor. Flame sensing must take place
within 4 seconds.
7. Once flame sense has been achieved, a timer on the
IFC starts and after the “Blower On” delay has
completed, the indoor blower will energize and run
at the 1
st
stage gas heating speed.
•
During this time, the variable speed inducer will
start its 1
st
stage learning routine, seen as
L
LR
R1
1
on the seven segment LED display.
X
Xt
t1
1
and
L
LR
R1
1
will alternately be displayed until the learning
routine has been successfully completed. See
Learning Routine section below for specifics.
8. Once the 1
st
stage learning routine has successfully
been achieved, the seven segment LED will
alternately read:
XtI
= Gas heating, Stage 1
ARF
= Airflow
060
= 600 requested cfm (value shown x 10)
9. When the temperature raises enough to satisfy the
thermostat setting, contacts R-W1 will open.
10. The gas valve relay will open, closing the gas valve.
The inducer will continue to run the post-purge for
approximately 5 seconds to remove any
combustion byproducts from inside the furnace.
11. The indoor blower continues to run the heat off
delay to remove heat from the heat exchangers.
The blower off time is field adjustable through the
IFC menu setup option. The seven segment LED will
read “
IDL
” = Idle, no thermostat demand.
2
2
n
nd
d
S
Stta
ag
ge
e G
Ga
ass H
He
ea
attiin
ng
g
N
No
otte
e:: 2
nd
stage heating cannot operate without 1
st
stage operation.
1. R – W1 contacts close on the thermostat sending
24VAC to the W1 low voltage terminal of the IFC.
Technician should read 24VAC from W1 to B/C. The
seven segment LED will read “
Xt1
”.
2. T
Th
he
e IIF
FC
C p
pe
errffo
orrm
mss a
a sse
ellff--cch
he
ecckk rro
ou
uttiin
ne
e a
an
nd
d tth
he
en
n
cco
on
nffiirrm
mss::
a. Condensate pressure switch and Inducer limit
switch are closed by sending 24VAC out the
HLO terminal and monitoring the ILI input.
b. Flame roll-out switches (FRS) 1 & 2, main
thermal limit (TCO), and any reverse air flow
(RAF) switches are closed by sending 24VAC out
the HLO terminal and monitoring the HLI input.
N
No
otte
e:: Downflow units will have one reverse air
flow switch (RAF).
Upflow units will have two reverse air
flow switches (RAF).
c. Pressure switch 1 (PS1) and pressure switch 2
(PS2) are opened by sending 24VAC out the
HLO terminal, through the limit switches, and
monitoring the PS1 and PS2 inputs.
N
No
otte
e:: If a thermal limit is open, 24VAC will not
be present at either pressure switch.
3. After steps 2a, b, and c are confirmed, the variable
speed inducer is energized and will run at the
predetermined factory default 1
st
stage inducer
speed. As the inducer ramps up, PS1 will close.
4. When PS1 closes, the ignitor relay on the IFC will
close. The ignitor is energized and warm up is
approximately 20 seconds.
