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31-5000734 Rev. 0
Heating Components
Ignitor
The ignitor is made of durable silicon nitride. Ignitor
longevity is enhanced by controlling voltage to the ignitor.
The integrated control provides a regulated 120 volts to the
ignitor for a consistent ignition and long ignitor life. Ohm
value should be 39 to 70. See Figure 13 for ignitor location
and Figure 14 for ignitor check out.
NOTE:
The NF80XV furnace contains electronic
components that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
Flame Sensor
A flame sensor is located on the top of the air gas plenum.
See Figure 13. The sensor can be removed for service
without removing the the burner. During operation, flame is
sensed by current passed through the flame and sensing
electrode. The control allows the gas valve to remain open
as long as flame signal is sensed. To check flame sense
signal use the push-button found on the integrated control
and go to Field Test Mode. The menu will display the flame
signal. See Table 14 for flame signal.
Normal
Low
Drop Out
2.6 or greater
2.5 or less
1.1
Table 14. Flame Signal in Microamps
Gas Valve
The valve (Figure 16) is internally redundant to assure
safety shut-off. If the gas valve must be replaced, the same
type valve must be used.
24VAC terminals and gas control knob are located on the
valve. A wire harness connects the terminals from the gas
valve to the electronic ignition control. 24V applied to the
terminals energizes the valve. Inlet and outlet pressure
taps are located on the valve. A regulator adjustment screw
is located on the valve.
Thermal Switch
The auto-reset switch is located on the front of the intake
air elbow. The switch will safely shut the unit down if
excessive temperatures are detected. See Figure 13.
When the switch senses excessive temperature, the circuit
breaks and the ignition control immediately stops ignition
and closes the gas valve.
Burner and Orifice
Burner is factory set and require no adjustment. Always
operate the unit with air gas plenum in place. The burner
has one orifice located between the gas valve and the
air intake assembly (Figure 13). To check or replace the
orifice remove the intake air screen, coupling and intake
air elbow.Using a 5/8” socket, go through the elbow and
unscrew the gas orifice. The burner uses an orifice (see
Table 15) that is precisely matched to the burner input.
The burner can be removed for service. If burner has been
removed, it is critical to replace all gaskets.
Unit Input
Orifice Size (0 - 4500 ft)
060
0.0595
080
0.0689
100
0.0810
Table 15.
Gas Orifices
Primary Limit Control (S10)
The primary limit (S10) is located in the heating vestibule
panel. When excess heat is sensed in the heat exchanger,
the limit will open. If the limit is open, the furnace control
energizes the supply air blower and closes the gas valve.
The limit automatically resets when unit temperature
returns to normal. The switch must reset within three
minutes or the control will go into Watch guard for one
hour. The switch is factory set and cannot be adjusted. The
switch may have a different set point for each unit model
number
