S9240F1004 MODULATING HOT SURFACE IGNITION INTEGRATED FURNACE CONTROL
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69-2088—01
— 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
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).
Indoor Blower Motor Failure
The IFC monitors communication from the indoor blower
motor and takes action for reduced airflow and failed motor
conditions as described below.
1.
Reduced circulating airflow operation (plugged filter, too
small duct, etc.) with RBC 3.0 Indoor Air Blower (IAB)
motor:
— In heating mode:
• The IFC calls for the CFM required to match the
target heat input rate.
• The IFC monitors continuously status of the motor
to insure adequate airflow for the target heating
input rate.
• RBC 3.0 motor provides constant airflow for a given
range of duct static pressure. When duct static
pressure exceeds the capability of the motor (for
example, due to a blockage), the motor enters a
power limiting mode called “cutback”. This
operation is internal to the motor logic and occurs
when the RPM required to achieve the target CFM
is higher than the motor’s capability.
• The IFC takes the following action when the RBC
3.0 motor reports the cutback mode operation:
(a) As soon as the motor enters cutback mode,
the IFC flashes the appropriate LED error
code.
(b) The IFC reduces the input rate by the
decrease amount shown in Table 8 and
adjusts the CFM to match. The appliance
continues to run at the new rate for a mini-
mum of one minute to allow the system to
stabilize.
- If the motor exits cutback mode, then the
IFC maintains this input rate as the maxi-
mum for the duration of the heat cycle, and
flashes the appropriate LED error code.
- If the motor does not exit cutback mode,
the IFC reduces the input rate by another
step and adjusts the CFM to match. This
sequence continues until the motor exits cut-
back mode.
(c) If the IFC has reduced the input rate down to
minimum (40%) and the RBC 3.0 motor is
still in cutback mode, the IFC shuts down the
furnace, activates the blower off delay,
enters soft lockout, and flashes the appropri-
ate LED error code.
— Cooling or Continuous Fan Mode:
• The IFC calls for the CFM required for cool stage or
continuous fan operation.
• The IFC continuously monitors the status of the
motor.
• The RBC 3.0 motor provides constant airflow for a
given range of duct static pressure. When duct
static pressure exceeds the capability of the motor,
the motor enters a power limiting mode called
“cutback”. This operation is internal to the motor
logic.
• The IFC continues normal cooling or continuous
fan operation but flashes an appropriate LED error
code if the motor enters cutback mode. The LED
error code displays for entire cycle, but is cleared
upon completion of the thermostat call for cooling.
2.
Failed RBC 3.0 Indoor Air Blower (IAB) motor (dead
motor, no power to motor, stuck wheel, no communica-
tions with motor, etc.)
— Standby Mode:
• The IFC continuously monitors for motor issues,
and flashes appropriate LED error codes. The IFC
takes no action on thermostat calls.
• The IFC clears the error code upon resolution of
the motor issue and proceeds with normal
operation.
— Heating Mode
• Upon call for heat – The IFC will not initiate call for
heat if a motor issue exists. The IFC flashes an
LED error code, and holds until the error clears.
• During call for heat – The IFC de-energizes the gas
valve, immediately turns off the blower, proceeds to
normal post purge, flashes an LED error code, and
holds until the error clears. (If communication is
down the motor may not receive the command.)
Inducer Motor Failure
The IFC constantly monitors the Inducer Motor current
consumption.
If the current is out of acceptable range (too high), action is
taken as follows:
— Over-current (current too high) – The IFC enters Soft
lockout and flashes the appropriate LED error code.
— A new ignition sequence initiates after the auto reset
from Soft Lockout.
NOTE: Under-current is not reported as an error.
Table 8. Indoor Blower Motor.
Motor HP
Cutback RPM
Firing Rate
Decrease Amount
1/2
1300
10%
1
1300
10%