30
3. Set the thermostat above room temperature and observe
the Operating Sequence.
4. Remove the close-off immediately after the limit switch
opens. If the furnace continues to operate with no return
air, set the thermostat below room temperature, shut
off power to the furnace, and replace the limit switch.
The fixed speed high efficiency blower kit is equipped with
a microprocessor control which is designed to provide a
variety of system airflows and comfort options. Before
operation, the fixed speed high efficiency blower must
be configured to match the unit with the system, system
options, and climate conditions. The blower is configured
by setting the 8 switches located on the motor control
board as described below.
IMPORTANT NOTE:
Selecting the (Gas) Heating Speed
The motor torque during heating is selected by setting
switches 1 through 4 (also marked as HEAT) on the motor
control board. Refer to
Table 8 (page 36) and select an
airflow to allow the furnace to reach an appropriate heat
rise as shown on the unit rating plate. NOTE: To reduce
the heat rise, select a higher airflow; to increase the heat
rise, select a lower airflow. Make sure that the selected
rise is within the specification of the furnace as shown on
the furnace rating label.
Determining Nominal System Capacity
In order to select the appropriate airflow for the AC and HP
operation, the nominal system capacity must be known.
The nominal system capacity is ALWAYS the nominal
capacity of the outdoor unit. In some cases, the nominal
system capacity is not the same as the nominal capacity
of the indoor coil.
Selecting the Cooling/Heat Pump Speed
The motor torque during cooling/heat pump is selected
by setting switches 5 through 8 (also marked as COOL)
on the motor control board. All motor torques for other
modes of operation, except for gas heat, are determined
by this setting. Refer to Table 8 and select an airflow in
the range recommended for the nominal system capacity.
For maximum capacity and energy efficiency, generally
a selection at or near the top of the CFM range for
that nominal system capacity is best. For maximum
dehumidification, select an airflow near the middle or
bottom of the CFM range for that nominal system capacity.
NOTE: If coil icing is observed, the cooling/heat pump
airflow may be set too low. Make sure the setting selected is
within the range shown. Also, verify the system is properly
charged (see outdoor unit installation instructions). If
icing continues to occur, raise the selected torque one
or two steps.
(Gas) Heating Mode
When the thermostat calls for heating, the circuit between
R and W is completed. The furnace control board initiates
the ignition sequence. Approximately 30 seconds after the
gas flame has proven, the blower motor will slowly ramp
up to the selected motor torque. The blower will continue
to operate after the call for heat has been removed for a
selectable (switch on furnace control board) number of
seconds. NOTE: All on- and off-delays for heating continue
to be controlled by the furnace control board.
Cooling or Heat Pump Mode
When the thermostat calls for cooling or heat pump heating,
the circuit between R, G, and Y (O is ignored by the blower)
is completed. The blower slowly ramps up to the selected
cooling motor torque. If there is a humidistat connected
to the motor control board calling for humidity control, the
motor will operate at 70% of the torque setting. Or, if the
system is installed where humidity control is desired but
a humidistat is not available, the DEHUM and R terminals
on the motor control board may be jumpered. In this
case, the blower will operate at 60% torque for the first
10 minutes of the cycle and then return to normal torque
for the remainder of the cooling cycle. After the call for
cooling or heat pump is satisfied, the blower continues
to operate for 60 seconds at half of the selected torque.
Manual Fan
When the manual fan switch on the thermostat is on,
(energizing G only) the blower will ramp up to 50% of the
selected cooling/heat pump motor torque.
Fault Conditions
There is a green and a red LED (labeled “Status”) on the
motor control board to provide system faults as described
below. Refer to Table 19 (page 55)) to determine motor
control board fault conditions.
OPERATING SEQUENCE
The operating sequences for the heating, cooling, and
fan modes are described below. Refer to the field and
furnace wiring diagrams: Figure 27 (page 27), Figure 28
(page 28)
, Figure 33 (page 40), and Figure 34 (page 41).
1. The thermostat calls for heat by energizing the W
terminal with 24VAC.
2. The control verifies the pressure switch is open.
3. If the pressure switch is open, the control energizes the
inducer and waits for the pressure switch to close. The
pressure switch must close within 10 seconds.
4. The control runs the inducer for a 30 second pre-purge.
5. The control energizes the Hot Surface Igniter (HSI)
output for the appropriate warm-up time limit.
6. The control energizes the main gas valve for 3 seconds.
7. If the flame proved and ignites the gas, the control de-
energizes the HSI. The gas valve and inducer remains
energized. The control goes to blower on delay.
8. If flame is present, the control energizes the blower on
the selected HEAT speed 30 seconds after the gas valve
opened. The gas valve and inducer remain energized.
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