Lennox ML180UHE Series - HEATING COMPONENTS; Flame Rollout Switches; Primary Limit Control; Flame Sensor

Page 12
HEATING COMPONENTS
Gaskets
Collector Box
Orifice Plate
Flue Transition
Pressure Switch
Combustion Air Inducer
Manifold And Gas Valve
Ignitor
Sensor
Rollout Switches
FIGURE 6
5. Flame Rollout Switches (Figure 6)
Flame rollout switch (S47) is a high temperature limit.
Each furnace 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 integrated control immediately stops ignition and clos-
es the gas valve. If unit is running and ame rollout is de-
tected, the gas valve will close and integrated control will
be disabled. Rollout can be caused by a blocked heat ex-
changer, blocked ue or lack of combustion air. The switch
has a factory setpoint of 210°F and cannot be adjusted.
To manually reset a tripped switch, push the reset button
located on the control.
6. Primary Limit Control
The primary limit on ML180UHE(X) units is located in the
heating vestibule panel under the combustion air induc-
er. See gure 7. When excess heat is sensed in the heat
exchanger, the limit will open. If the limit is open, the in-
tegrated control energizes the supply air blower and clos-
es the gas valve. The limit automatically 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 di󰀨erent setpoint for each unit model number. If limit
switch must be replaced, refer to Lennox ProductZone re-
pair parts list.
Primary Limit Under Combustion Air Inducer
Primary
Limit
FIGURE 7
7. Flame Sensor (Figure 6)
A ame sensor is located on the left side of the burner sup-
port. The sensor is mounted on the ame rollout plate and
the tip protrudes into the ame envelope of the left-most
burner. The sensor can be removed for service (clean
with steel wool) without removing any part of the burn-
ers. During operation, ame is sensed by current passed
through the ame and sensing electrode. The integrated
control allows the gas valve to remain open as long as
ame signal is sensed.
A microamp DC meter is needed to check the ame signal
on the integrated control.