Lennox KGC Series Unit Information page 23

3-Flame Rollout Limits S47
Flame rollout limit S47 is a SPST N.C. high temperature
limits located just above the burner air intake opening
in the burner enclosures (FIGURE 12). S47 is wired to
the ignition control A3. When S47 senses flame rollout
(indicating a blockage in the combustion air passages),
the ignition control immediately closes the gas valve.
Limit S47 is factory preset to open at 290
+ 6.7C) on a temperature rise in all units. All flame rollout
limits are manual reset.
4-Primary High Temperature Limit S10
S10 is a SPST N.C. high-temperature primary limit for gas
heat in all units. S10 is located next to the blower. See
FIGURE 13.
Primary limit S10 is wired to the ignition control A3. Its
N.C. contacts open to de-energize the ignition control
when excessive temperature is reached in the blower
compartment. If the limit trips, the blower relay coil K3
will be energized by ignition control A3. Three limits with
different actuating temperatures are used for limits S10.
Use appropriate limit when replacement is required.
FIGURE 13
5-Combustion Air Prove Switches S18
Prove switch S18 is a SPST N.O. switch located to the right
of the induced draft assembly. S18 monitors combustion
air inducer operation. Switch S18 is wired to the ignition
control A3. The switch closes on a negative pressure fall.
This negative pressure fall and switch actuation allows the
ignition sequence to continue (proves, by closing, that the
combustion air inducer is operating before allowing the gas
valve to open.) The combustion air prove switch is factory-
set and is not adjustable. The switch will automatically
open on a pressure rise (less negative pressure). TABLE
3 shows prove switch settings.
F + 12 F (143C
o o
S10 LIMIT LOCATION
Page 23
TABLE 3
S18 Prove Switch Settings
Close" wc (Pa)
0.25 + 5 (62.3+12.4)
6-Combustion Air Inducers B6
Combustion air inducers on KGC units provide air to the
corresponding burners while clearing the combustion
chamber of exhaust gases. The inducer begins operating
immediately upon receiving a thermostat demand and is
de-energized when thermostat demand is satisfied.
The inducer uses a 208/230V single-phase PSC motor
and a 4.81in. x 1.25in. (122mm x 32mm) blower wheel.
All motors operate at 3200RPM and are equipped with
autoreset overload protection. Inducers are supplied by
various manufacturers. Ratings may vary by manufacturer.
Specific inducer electrical ratings can be found on the
unit rating plate. On a heating demand (W1), the ignition
control A3 initiates the heating cycle. A3 then allows 30
seconds for the combustion air inducer to vent exhaust
gases from the burners.
When the combustion air inducer is purging the exhaust
gases, the combustion air prove switch closes, proving that
the combustion air inducer is operating before allowing
the ignition sequence to continue. When the combustion
air prove switch is closed and the delay is over, the ignition
control activates the first-stage operator of the gas valve
(low fire), the spark and the flame sensing electrode.
Sparking stops immediately after flame is sensed or at the
end of the eight-second trial for ignition. All combustion
air inducer motors are sealed and cannot be oiled. The
inducer is not adjustable; but, it can be disassembled for
cleaning.
7-Combustion Air Motor Capacitors C3
The combustion air inducer motors in all KGC units require
run capacitors. Capacitor C3 is connected to combustion
air inducer B6. Ratings will be on the side of capacitor or
combustion air motor nameplate.
Close" wc (Pa)
0.10+5 (24.8+12.4)