508033-02 Issue 2135 Page 27 of 48
Combustion Air Inducer (B6)
All A80US2VX 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
rststage heat, then switches to high speed for second
stage heat.
Combustion Air Inducer Prove Switch (S18)
A80US2VX series units are equipped with a single
combustion air proving switch (rst 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 ue becomes obstructed.
On heat demand (rst 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 A80US2VX models. The pressure sensed by
the switch is negative relative to atmospheric pressure. If
the ue becomes obstructed during operation, the switch
senses a loss of pressure dierence and opens the circuit
to the furnace control and gas valve.
COMBUSTION AIR PRESSURE SWITCH
Positive +
to air intake pipe
Negative -
to air intake
elbow
Figure 15.
NOTE: The switch is factory set and is not eld 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 eld 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.
A80US2VX 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 o 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 ve 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.
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