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31-5000734 Rev. 0
Combustion Air Inducer (B6)
All NF80XV units use a two-stage combustion air inducer
to move air through the burners and heat exchanger during
heating operation. The blower uses a 120VAC motor.
The motor operates during all heating operation and is
controlled by integrated control control A92. The inducer
also operates for 15 seconds before burner ignition
(prepurge) and for 5 seconds after the gas valve closes
(postpurge). The inducer operates on low speed during
firststage heat, then switches to high speed for second
stage heat.
Combustion Air Inducer Prove Switch (S18)
NF80XV series units are equipped with a single combustion
air proving switch (first and second stage) located near
the gas valve. See Figure 15. The switch is a single-pole
single-throw proving switch electrically connected to the
integrated control. The purpose of the switch is to prevent
burner operation if the combustion air inducer is not
operating or if the flue becomes obstructed.
On heat demand (first or second stage) the switch senses
that the combustion air inducer is operating. It closes a
circuit to the integrated control when pressure inside the
combustion air inducer decreases to a certain set point.
The set point is 0.20” for low heat and high heat and the
same for all NF80XV models. The pressure sensed by
the switch is negative relative to atmospheric pressure. If
the flue becomes obstructed during operation, the switch
senses a loss of pressure difference and opens the circuit
to the furnace control and gas valve.
COMBUSTION AIR PRESSURE SWITCH
Po
to air intake pipe
Negative -
to air intake
elbow
Figure 15.
NOTE:
The switch is factory set and is not field adjustable.
It is a safety shut-down control in the furnace and must
not be by-passed for any reason. If switch is closed or
bypassed, the control will not initiate ignition at start up.
Placement and Installation
Make sure unit is installed in accordance with installation
instructions and applicable codes.
Start-Up
Preliminary and Seasonal Checks
1.
Inspect electrical wiring, both field and factory installed
for loose connections. Tighten as required.
2. Check voltage at disconnect switch. Voltage must be
within range listed on the nameplate. If not, consult the
power company and have voltage condition corrected
before starting unit.
Heating Start-Up
Shock and burn hazard.
NF80XV units are equipped with a hot surface ignition
system. Do not attempt to light manually.
WARNING
1.
STOP!
Read the safety information at the beginning
of this section.
2. Set the thermostat to the lowest setting.
3.
Turn off all electrical power to the unit.
4. This furnace is equipped with an ignition device which
automatically lights the burners. Do not try to light the
burners by hand.
5. Remove the access panel.
6. Turn switch on gas valve to OFF. Do not force. See
Figure 16.
7.
Wait five minutes to clear out any gas. If you then
smell gas,
STOP!
Immediately call your gas supplier
from a neighbor’s phone. Follow the gas supplier’s
instructions. If you do not smell gas go to next step.
