80
S8V2-SVX001-1A-EN
Sequence of Operation
NNoottee:: The seven-segment LED readout is based on
thermostat input. A simultaneous call for W1 and
W2, the seven-segment LED will read “
Xt1
”, the
IFC will process the call for 1
st
stage heat, then
transition to “
Xt2
” after the interstage delay
timing has completed.
AACCCC11 ((EEAACC)) aanndd AACCCC22 ((HHUUMM)) TTiimmiinngg
• EAC relay closes approximately 2 seconds after the
blower motor starts.
• EAC relay opens when the blower motor stops.
• HUM relay closes on any heating call (HP/Gas)
approximately 1 second after the blower motor
starts.
• HUM relay opens when the heating call (HP/Gas) is
removed.
11
sstt
SSttaaggee GGaass HHeeaattiinngg
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. The IFC performs a self-check routine and then
confirms that the:
a. 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.
b. Pressure switch 1 (PS1) and pressure switch 2
are open by sending 24VAC out the PSO
terminal and monitoring the PS1 and PS2
inputs.
3. After steps a & b are confirmed, the inducer relay is
closed energizing the inducer motor.
4. As the inducer ramps up, PS1 will close.
NNoottee:: The inducer motor starts on high speed for
approximately 6 seconds, then switches to low
speed. If PS1 does not close within 60 seconds,
the control will report a
E3
.
2
error and increase
the inducer to high speed in an attempt to close
PS1 & PS2. In this error state, 2
nd
stage heat will
operate with a W1 call only. When PS1 closes,
the igniter relay on the IFC will close and the
igniter is energized. The igniter warm up is
approximately 17 seconds.
5. After the igniter warm up, the 1
st
stage gas valve
relay is closed, which energizes 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. Proof of flame must be
established within 4 seconds.
NNoottee:: There are two flame sense pads located on the
IFC marked as “FP”. To measure the flame
current, use a VOM set to DC volts. 1VDC = 1
micro-amp. Flame current will vary depending
on the type of meter used. Typical flame current
ranges from 0.75 – 3.0 micro-amps (0.75 – 3 VDC).
7. Once flame sense has been established, a timer on
the IFC starts, and the indoor blower will energize at
1st stage speed after the blower “Heat On Delay”
has completed. The seven-segment LED for
example will alternately read:
• Xt1 = Gas heating, stage 1
• ARF = Airflow
• 080 = 800 calculated cfm (value shown x 10)
8. When the temperature raises enough to satisfy the
thermostat setting, contacts R-W1 will open.
9. The gas valve relay will open, closing the gas valve.
The inducer will continue to run for approximately 5
seconds to remove any combustion byproducts
from inside the furnace.
10. The indoor blower continues to run 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 1 DL = Idle, no
thermostat demand.
22
nndd
SSttaaggee GGaass HHeeaattiinngg
1. See sequence of operation for 1
st
stage gas heating
operation above (steps 1-8)
NNoottee:: 2
nd
stage heating cannot operate without 1
st
stage operation.
2. R-W2 contacts close on the thermostat sending
24VAC to the W2 low voltage terminal of the IFC.
Technician should read 24VAC from W2 to B/C. The
seven-segment LED will read Ht2.
3. The IFC energizes the 2
nd
stage inducer relay. The
inducer is energized on high speed, and the second
stage gas valve relay on the IFC closes, energizing
second stage gas valve. The indoor blower motor
will ramp up to the 2
nd
stage gas heating speed.
The seven-segment LED for example will
alternately read:
• Xt2 = Gas heating, Stage 2
• ARF = Airflow
• 112 = 1120 calculated cfm (value shown x 10)
4. The IFC monitors PS2 for closure and if PS2 does
not close within 45 seconds, a PS2 open error will
be declared and the furnace will operate in 1
st
stage. If PS2 closes, 2
nd
stage gas heating will
continue until the thermostat R-W2 contacts open.
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