88-A801X001-1B-EN
55
Sequence of Operation
N
No
otte
e:: The seven-segment LED readout is based on
thermostat input.
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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: .
•
Xt
2. The IFC performs a self-check routine and then
confirms:
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. The pressure switch is opened by sending
24VAC out the HLO terminal, through the limit
switch, and monitoring the PS input.
N
No
otte
e:: If a thermal limit is open, 24VAC will not
be present at the pressure switch.
3. After steps a & b are confirmed, the inducer relay is
closed, energizing the inducer motor.
4. As the inducer ramps up, PS will close.
5. When PS closes, the ignitor relay on the IFC will
close. The ignitor is energized. The ignitor warm up
is approximately 17 seconds.
6. After the ignitor warm up, the gas valve relay is
closed, which energizes the gas valve solenoid to
allow ignition.
7. The first burner will ignite, and flame will crossover
to the remaining burners establishing current to the
flame sensor. Flame sensing must be established
within 4 seconds.
N
No
otte
e:: 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).
8. Once the flame sense has been established, a timer
on the IFC starts and the indoor blower will energize
after the blower “Heat On Delay” has completed.
The seven-segment LED for example will
alternately read:
•
Xt
= Gas heating
•
tP5
= Tap 5
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 for approximately 5
seconds to remove any combustion byproducts
from inside the furnace.
11. 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 “
IDL
” = Idle, no
thermostat demand.
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1. R-Y1-G contacts on the thermostat close sending
24VAC to the Y1 and G low voltage terminals on the
IFC. Technician should read 24VAC between Y1-B/C
and between G-B/C.
2. 24VAC is sent to the OD unit via thermostat wiring.
3. The indoor blower ramps to the cooling airflow.
The seven-segment LED for example will
alternately read:
•
CP1
= Cooling / Heat Pump
•
tP7
= Tap 7
4. When the temperature is lowered / raised (HP
mode) enough to satisfy the thermostat setting,
contacts R-Y-G will open.
5. The OD unit shuts off and the indoor blower shuts
off, unless a blower “Cool Off Delay” has been
enabled in the IFC setup menu options. The seven-
segment LED will read “
IDL
” = Idle, no thermostat
demand.
