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ML180UHA HEATING COMPONENTS
FIGURE 6
Gasket
Collector Box
Orifice Plate
Flue Transition
Pressure Switch
Combustion Air Inducer
Manifold And Gas Valve
Ignitor
Sensor
Rollout Switches
5. Flame Sensor (Figure 6)
A flame sensor is located on the left side of the burner sup
port. The sensor is mounted on the flame rollout plate and
the tip protrudes into the flame envelope of the left-most
burner. The sensor can be removed for service without re
moving any part of the burners. During operation, flame is
sensed by current passed through the flame and sensing
electrode. The integrated control allows the gas valve to re
main open as long as flame signal is sensed.
6. Flame Rollout Switches (Figure 6) (S47)
Flame rollout switch is a high temperature limit. Each fur
nace is equipped with two identical switches. The limit is a
N.C. SPST manual‐reset limit connected in series with the
integrated control A92. When S47 senses rollout, the inte
grated control immediately stops ignition and closes the
gas valve. If unit is running and flame rollout is detected, the
gas valve will close and integrated control will be disabled.
Rollout can be caused by a blocked heat exchanger, flue or
lack of combustion air. The switch has a factory setpoint of
99°C (210°F) and cannot be adjusted. To manually reset a
tripped switch, push the reset button located on the control.
7. Primary Limit Control (S10)
The primary limit on ML180UHA units is located in the heating
vestibule panel under the combustion air inducer. See figure 1.
When excess heat is sensed in the heat exchanger, the limit
will open. If the limit is open, the integrated control energizes
the supply air blower and closes the gas valve. The limit auto
matically resets when unit temperature returns to normal. The
switch must reset within three minutes or SureLight
®
control
will go into Watchguard for one hour. The switch is factory
set and cannot be adjusted. The switch may have a different
setpoint for each unit model number. If limit switch must be
replaced, refer to Lennox ProductZone repair parts list on
Lennox DaveNet®.
