Allied A80UH1EX - Page 11

508031-02 Issue 2135 Page 11 of 29
Combustion Air Inducer (B6)
All A80UH1EX & 80G1UHEX units use a 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 A92. The inducer also
operates for 15 seconds before burner ignition (pre-purge)
and for 5 seconds after the gas valve closes (post-purge).
Combustion Air Inducer Prove Switch (S18)
A80UH1EX & 80G1UHEX series units are equipped with
a combustion air pressure switch (Figure 7) located near
the gas valve. The switch is connected to the combustion
air inducer housing by means of a exible silicone hose. It
monitors negative air pressure in the intake air elbow.
The switch is a single-pole single-throw proving switch
electrically connected to the furnace 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 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 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 di󰀨erence and opens the circuit
to the furnace control and gas valve. See Table 6 for set
point.
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.
Model Make in. w.c. Break in. w.c.
All 0.35 0.20
Table 6. Prove Switch Set Points
Positive +
to air intake pipe
Negative -
to air intake
elbow
Figure 7. Combustion Air Pressure Switch
Ignitor (Figure 6)
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 8 for resistance, and voltage check.
NOTE: The A80UH1EX & 80G1UHEX furnaces contain
electronic components that are polarity sensitive. Make
sure that the furnace is wired correctly and is properly
grounded.
Burner and Orice
Burners are factory set and require no adjustment. Always
operate the unit with air gas plenum in place. The burner
has one orice located between the gas valve and the air
intake assembly (Figure 6). To check or replace the orice
remove the intake air screen, coupling and intake air elbow.
Using a 5/8” socket, go through the elbow and unscrew the
gas orice. The burner uses an orice (see Table 7) 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 Orice Size
040
0.0595
060
080 0.0689
100 0.0810
Table 7. Gas Orice