S9240F2051 MODULATING INTEGRATED FURNACE CONTROL
69-2807—01 16
• The IFC flashes an LED error code indicating there
is a hardware malfunction.
— If voltage is no longer detected on the valve for more
than the fault debouncing time:
• The IFC proceeds to Postpurge and de-energizes
the circulator after the selected heat off delay.
• After Postpurge the IFC proceeds to normal
operation.
— If the inducer is energized and the main valve relay
contacts are sensed closed even though the relay is
not energized (welded contacts):
• The IFC flashes an LED error code indicating there
is a hardware malfunction.
• The inducer immediately switches off in an attempt
to open the pressure switch.
• If, after 5 seconds, flame is sensed or voltage is
sensed on the main valve, the IFC energizes the
inducer at ignition fire rate speed and the circulator
on mid heat speed.
• If flame is not sensed and voltage on the main valve
is no longer sensed, the IFC proceeds to a Soft
Lockout where it remains for the Auto Restart Delay
period.
— If voltage is not detected on the valve for longer than
the fault debouncing time during a period when the
valve is to be energized (contacts failed to make):
• The IFC proceeds as if flame is not sensed.
• If Soft Lockout is entered due to this condition, the
IFC flashes an LED error code indicating failed
hardware.
Flame Out of Sequence
The IFC does not take action on flame sensed in Idle Mode
when there is no call for heat present.
If the IFC is servicing a call for heat and flame is sensed when
it is not expected to be present, the ignition and fan
sequences are not allowed to progress and the IFC remains in
its current state. The exception is Igniter Warm-up where the
IFC proceeds to Prepurge.
If the sensed flame goes away before the Flame Debounce
Period, the ignition sequence proceeds as normal. If however,
the sensed flame lasts longer than the Flame Debounce
Period:
— The igniter de-energizes.
— The inducer energizes at ignition fire rate speed, and
the circulator energizes at mid heat speed.
— The IFC flashes an LED error code indicating the
flame is sensed out of sequence.
— Once the sensed flame goes away, the IFC proceeds
to Postpurge followed by Soft Lockout with a flashing
LED error code. The Soft Lockout error code is cleared
when Idle Mode is entered.
Line Voltage Sensing
Line voltage sensing is used only for HSI voltage regulation.
Line voltage is measured between L1 and Neutral. The level
of the line voltage input is monitored at all times.
— If line voltage is measured to be less than 90V RMS
(+/- 5%):
• The IFC proceeds to Soft Lockout and flashes an
LED error code indicating low line voltage.
• Calls for cooling and fan are serviced while low
voltage is sensed.
— If line voltage is measured to be greater than 150V
RMS (+/- 5%):
• The IFC proceeds to Soft Lockout and flashes an
LED error code indicating high line voltage.
• Calls for cooling and fan are serviced while high
voltage is sensed.
Cool and fan operation is not affected by low/high line voltage.
In heating mode, if a high or low line voltage condition is
detected, the heating cycle ends. If the circulator is running, it
turns off after the heat off delay.
The presence of an earth ground or reversed line polarity has
no effect on flame sensing. The IFC does require an electrical
connection between the transformer common and the burner
to ensure proper flame sensing. This electrical connection is
to be provided in the appliance wiring harness and is not
monitored by the IFC.
Weak Flame Sensing
After a successful Trial for Ignition, while operating at any firing
rate, if the IFC senses a weak flame signal for longer than the
fault debouncing time:
• The IFC flashes an LED error code indicating there
is a poor flame signal. A strong flame must be
sensed for longer than the fault debouncing time or
the heat demand must be removed to clear the
error code.
Hot Surface Igniter (HSI) Sensing
— If the HSI is open-circuited or the associated circuitry
is no longer capable of energizing the HSI:
• The IFC flashes an LED error code indicating a
failed ignition circuit and proceeds to Soft Lockout
where it remains for the Auto Restart Delay period.
• If the inducer is energized at the time the fault is
detected, it remains on for a 15 second purge
period before the IFC proceeds to Soft Lockout.
— If the HSI triggering circuitry is sensed as shorted
while waiting for the low pressure switch to close or
during Prepurge:
• The inducer immediately de-energizes.
• The IFC flashes an LED error code indicating an
internal error.
Resets From Lockout
The IFC is reset from Lockout by any one of the following
three ways:
— Cycling power – Remove power for longer than 10
seconds.
— Thermostat Reset – Remove the call for heat for
longer than three seconds but less than 20 seconds.
— Auto Restart (Soft Lockout only) – The IFC
automatically exits Soft Lockout after the Auto Restart
Delay expires (assuming the fault that sent the IFC to
Soft Lockout has cleared).
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