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• This process repeats until the calibration routine is
successful or the call for heat ends.
— If the low pressure switch opens for less than two
seconds during Prepurge or Igniter warm-up:
• The IFC completes the ignition sequence.
• If the appliance fails to light after the maximum
number of retries has been exceeded, the IFC
proceeds to Soft Lockout and attempts the
pressure switch calibration routine.
— If the low pressure switch opens for longer than two
seconds during Trial for Ignition or normal operation
(Run Mode):
• The IFC proceeds to Postpurge followed by the
vent calibration sequence, before attempting the
ignition sequence again.
• The IFC flashes an LED error code indicating the
pressure switch failed open until the vent
calibration sequence begins.
See Table 12 on page 27 for LED error code and lockout
information.
High Pressure Switch Operation (during heat
cycle)
The high pressure switch determines the inducer speed
required to achieve the high firing rate of the appliance. The
determination is made by the IFC during the calibration
process.
The high fire pressure switch should remain closed during
high fire operation.
— If it opens during high fire operation, the IFC increases
the inducer speed, up to the maximum allowed RPM,
in an attempt to re-close the high pressure switch.
— If the high pressure switch re-closes successfully, the
IFC completes the Heat mode, and performs the vent
calibration on the next call for heat.
— If the high pressure switch remains open, the IFC ends
the call for heat and performs the pressure switch
calibration routine.
The high pressure switch check takes place during calibration.
If the switch is stuck open or closed, calibration will not be
completed and the IFC flashes an error code.
See Table 12 on page 27 for LED error code and lockout
information.
Hot Surface Igniter (HSI) Control
The Hot Surface Igniter is voltage controlled to maintain 95V
+/- 5% over a range of 98 to 132V line input. The HSI warm up
time is fixed for all ignition trials. Both the continuity of the
igniter and the ability of the triggering circuit to energize the
igniter are continuously monitored during the Igniter Warm-up
and Ignition Activation periods. If a problem is detected, the
IFC flashes an LED error code.
See Table 12 on page 27 for LED error code and lockout
information.
S9240F1004 MODULATING HOT SURFACE IGNITION INTEGRATED FURNACE CONTROL
15
Humidity Control
Humidity control is available via line voltage or low voltage
operation.
Line Voltage Humidifier
The line voltage humidifier output is energized when either of
the following conditions are met:
— Anytime both the inducer and circulator are energized
and there is no cool request present.
— A request for compressor heat is active.
Low Voltage Humidifier
The H terminal on the thermostat block
connection to a 24 volt humidifier. The 24 Vac power is
supplied by the system transformer.
The IFC energizes the H terminal with 24 volts when either of
the following conditions are met:
— Anytime both the inducer and circulator are energized
and there is no cool request present.
— A request for compressor heat is active.
Standard Dehumidification
The dehumidification jumper
standard dehumidification.
The DS terminal on the thermostat block must connect to the
dehumidification output on a conventional thermostat or to the
DS output of a Harmony Zoning Control.
The IFC varies circulator speed operation based on the DS
signal from the thermostat or Harmony Zoning Control. Refer
to the "Harmony III Operation" for operation with Harmony.
Harmony III Operation
The dehumidification jumper
with the Harmony III zone control. Once this jumper is clipped,
the presence of a Harmony system versus a standard
dehumidification control is automatically detected by the IFC.
When the IFC is properly connected to a Harmony III zone
control operation is as follows:
— Switches 1 and 2 on DIP switch S1, which configure
the IFC for operation with various types of
thermostats, are ignored.
— The discharge air sensor is ignored.
— Circulator fan speed is determined by the PWM signal
on the DS terminal.
— Upon a call for heat with Harmony III present, the IFC
follows the proprietary Lennox modulating firing rate.
Electronic Air Cleaner
The line voltage EAC output energizes anytime the circulator
is energized, regardless of speed.
a
See "Wiring Connections - Class 2 - Low Voltage." on
page 4.
b
See jumper W914 in Table 4 on page 7.
a
is available for
b
must be clipped to enable
b
must be clipped for operation
69-2088—01
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