Page 9
31-5000723 Rev. 0
Unit Components
NF97UM unit components are shown in Figure 1. The gas
valve, combustion air inducer and burners can be accessed
by removing the access panel. Electrical components are in
the control box (Figure 2) found in the blower compartment.
NF97UM units are factory-equipped with a bottom return air
panel in place. The panel is designed to be field removed as
required for bottom air return. Markings are provided for side
return air and may be cut out in the field.
Electrostatic discharge can affect
electronic components. Take precautions
to neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
CAUTION
Control Box
Control Transformer (T1)
A transformer located in the control box provides power to the
low voltage section of the unit. Transformers on all models
are rated 40VA with a 120V primary and a 24V secondary.
Transformer
Integrated Control
Interlock Switch
Circuit Breaker
Figure 2. Control Box
Door Interlock Switch (S51)
A door interlock switch rated 14A at 125VAC is wired in
series with line voltage. When the inner blower access panel
is removed the unit will shut down.
Circuit Breaker (CB8)
A 24V circuit breaker is also located in the control box. The
switch provides overcurrent protection to the transformer
(T1). The breaker is rated 3A at 32V. If the current exceeds
this limit the breaker will trip and all unit operation will
shutdown. The breaker can be manually reset by pressing
the button on the face. See Figure 3.
PRESS TO RESET
Figure 3. Circuit Breaker CB8
Shock hazard.
Disconnect power before servicing. Integrated control is
not field repairable. If control is inoperable, simply replace
entire control.
Can cause injury or death. Unsafe operation will result if
repair is attempted.
WARNING
Integrated Control (A92)
Units are equipped with a variable capacity integrated
control. The control can operate with a
24V
conventional
single or two-stage thermostat. The system consists of an
ignition / blower control (Figure 4 and Figure 5) with control
pin designations (Table 1 through Table 2) and an ignitor.
The control and ignitor work in combination to ensure
furnace ignition and ignitor durability. The control provides
gas ignition, safety checks and indoor blower control with
two-stage gas heating. The furnace combustion air inducer,
gas valve and indoor blower are controlled in response to
various system inputs such as thermostat signal, pressure
and limit switch signal and flame signal. The control features
a seven-segment LED display, indicating furnace status
(including indoor blower) and error codes. The LED flashes
in single digits. For example, using the table on Page 18,
under CODE, an “E” followed by “2” followed by “5” followed
by “0”, the limit switch circuit is open. The control has a 120V
humidifier and a 120V accessory terminal, both rated at (1)
one amp each.
