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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.
Table 8. Indoor Blower Motor.
Motor HP
Cutback RPM
1/2
1300
3/4
1300
1
1300
1. Reduced circulating airflow operation (plugged filter, too
small duct, etc.).
— 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.
• The ECM 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 ECM
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
minimum of one minute to allow the system
to stabilize.
• If the motor exits cutback mode, then the IFC
maintains this input rate as the maximum 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 cutback mode.
(c)If the IFC has reduced the input rate down to
minimum (40%) and the ECM motor is still in
cutback mode, the IFC shuts down the
furnace, activates the blower off delay, enters
soft lockout, and flashes the appropriate 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.
S9240F2051 MODULATING INTEGRATED FURNACE CONTROL
Firing Rate
Decrease Amount
10%
10%
10%
17
• The ECM 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 ECM Indoor Air Blower (IAB) motor (dead motor,
no power to motor, stuck wheel, no communications
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.
Check Safety Shutoff Operation
1. Shut off the gas supply at the manual gas valve ahead
of the appliance.
2. Set the thermostat to call for heat. System should
operate as indicated in Fig. 9 on page 18 or Fig. 12 on
page 21.
3. Following lockout, open the manual gas valve and make
sure no gas is flowing to the burner.
This completes the Checkout procedures.
OPERATING SEQUENCES
Figures 9 through 14 beginning on page 18 describe the
various operating cycles (Light Off, Heat, Run, Cool, and Fan)
of the S9240F2051 Integrated Furnace Control (IFC).
69-2807—01
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