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3-Primary High Temperature Limit S10
S10 is a SPST N.C. high temperature primary limit for gas
heat in KGB024-090 units. S10 is located on the vestibule
panel. See figure 16.
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. Limit set points are factory set and
cannot be adjusted.
4-Flame Rollout Limit Switch S47
Flame rollout limit switch S47 is a SPST N.C. high temper
ature limit located just above the burner air intake opening in
the burner enclosures (see figure 17 ). S47 is wired to the igni
tion control A3. When S47 senses flame rollout (indicating
a blockage in the combustion air passages), the flame
rollout limit trips, and the ignition control immediately
closes the gas valve.
Limit S47 is factory preset to open at 340_F +
16_F on a
temperature rise on all units. All flame rollout limits are manu
al reset.
5-Combustion Air Prove Switch S18
Prove switch S18 is a SPST N.O. switch located to the right of
the induced draft assembly. S18 monitors combustion air in
ducer operation. Switch S18 is wired to the ignition control A3.
The switch closes at negative 0.10”W.C. +
0.05” (24.8 Pa +
12.4 Pa) on pressure fall. This negative pressure fall and
switch actuation allows the ignition sequence to continue
(proves, by closing, that the combustion air inducer is oper
ating before allowing the gas valve to open.) The combus
tion air prove switch is factory set and not adjustable.
6-Combustion Air Inducer B6
Combustion air inducers provide air to the corresponding
burners while clearing the combustion chamber of exhaust
gases. The inducer begins operating immediately upon re
ceiving a thermostat demand and is de-energized when
thermostat demand is satisfied.
The inducer uses a 208/230V single‐phase PSC motor and a
5.24 in. x .96in. blower wheel. All motors operate at 3300RPM
and are equipped with auto‐reset 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 to seconds for the combustion
air inducer to vent exhaust gases from the burners. When
the combustion air inducer is purging the exhaust gas
es, 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 immediate
ly after flame is sensed or at the end of the eight second
trial for ignition.
On two stage natural gas units the inducer will operate
on low speed for first stage heat (W1) and ramp up to
high speed for second stage heat (W2).
All combustion air inducer motors are sealed and cannot
be oiled. The inducer cannot be adjusted but can be dis
assembled for cleaning.
7-Combustion Air Motor Capacitor C3
The combustion air inducer motors in all KGA/KGB units
require run capacitors. Capacitor C3 is connected to
combustion air inducer B6. Ratings will be on side of ca
pacitor or combustion air motor nameplate.
8-Gas Valves GV1
Units are equipped with a single stage gas valve (figure 20) or
two stage gas valve (figure 21). On a call for first stage heat
(low fire), the valve is energized by the ignition control simulta
neously with the spark electrode. On a call for second stage
heat (high fire), the second stage operator is energized directly
from A3. A manual shut-off knob is provided on the valve
for shut-off. Manual shut‐off knob immediately closes both
stages without delay. On both valves first stage (low fire) is
quick opening (on and off in less than 3 seconds).
9-Spark Electrode (Ignitor) Figure 18
An electrode assembly is used for ignition spark. The
electrode is mounted through holes under the right most
burner location. The electrode tip protrudes into the
flame envelope of the adjacent burner. The electrode as
sembly is fastened to burner supports and can be removed for
service without removing any part of the burners.
During ignition, spark travels through the spark electrode (fig
ure 18) and ignites the right burner. Flame travels from burner
to burner until all are lit.
The spark electrode is connected to the ignition control by a 8
mm silicone‐insulated stranded high voltage wire. The wire us
es 1/4” (6.35 mm)female quick connect on both ends of the
wire.
NOTE - If electrode wire must be replaced, wire and
suppression must be same type cable.
The spark electrode assembly can be removed for inspection
by removing the screw securing the electrode assembly and
sliding it out of unit.
For proper unit operation, electrodes must be positioned and
gapped correctly.
Spark gap may be checked with appropriately sized twist drills
or feeler gauges. Disconnect power to the unit and remove
electrode assembly. The gap should be between 0.125” +
0.015” (3.2 mm + .4 mm). See figure 18.
IMPORTANT
In order to maximize spark energy to electrode, high
voltage wire should touch unit cabinet as little as
possible.
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