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S21 is also wired in series with the ignition control. It func
tions in the same manner as S10 but is factory set to trip at
140F +6F on a temperature rise and automatically reset
at 100F +7F on a temperature fall. This is a secondary
safety shut-down function of the unit.
In dual heat exchanger models, both heat exchangers are
disabled when S21 opens. In fifteen ton and larger units,
the combustion air blower(s) continue to operate when
S21 opens.
F-Flame Rollout Switch S47
Flame rollout switch S47 is a high temperature cutoff fuse
located just above the right burner air intake opening in the
burner compartment. The N.C. limit is connected in series
with ignition control A3. When S47 senses flame rollout (in
dicating a blockage in the combustion air passages), S47
trips, the ignition control immediately stops ignition and
closes the gas valve. The switch is factory set to trip at
171F and cannot be adjusted. The limit is a ceramic non-
resettable fusible link which must be replaced after being
tripped.
In units equipped with dual heat exchangers, S47 is lo
cated in the first stage heat exchanger. Both heat ex
changers are disabled when S47 opens. In fifteen ton and
larger units, the combustion air blower(s) continue to oper
ate when S47 opens.
G-Flame Rollout Switch S69
Rollout switch S69 is only used in units equipped with dual
heat exchangers. S69 is identical to rollout switch S47 but
is located in the second stage heat exchanger. Both heat
exchangers are disabled when S69 opens. In fifteen ton
and larger units, the combustion air blower(s) continue to
operate when S69 opens.
H-Combustion Air Prove Switch S18
The combustion air prove switch (S18) is a SPST N.O. cen
trifugal switch inside the combustion air motor. It is used to
monitor combustion air blower operation. The switch is
wired in series with ignition control A3. On startup, the
switch closes when the combustion air motor reaches be
tween 1850 and 2500 RPM to allow power to the ignition
control (proves, by closing, that the combustion air blower is
operating before allowing the ignition control to energize).
At the end of a heating demand (when combustion air mo
tor is de-energized), S18 opens when the combustion air
motor slows 50 to 450 RPM below the make." The com
bustion air prove switch is factory set and is not adjustable.
In dual heat exchanger models, S18 proves combustion air
blower operation in the first stage heat exchanger.
I-Combustion Air Prove Switch S45
Prove switch S45 is only used in units equipped with dual
heat exchangers. S45 is identical to S18. S45 proves com
bustion air blower operation in the second stage heat ex
changer.
J-Combustion Air Blower B6, B15
The combustion air blower provides fresh air to the burner
while clearing the combustion chamber of exhaust gases.
The blower begins operating immediately upon receiving
a thermostat demand and is de-energized immediately
when thermostat demand is satisfied. In dual heat ex
changer models, B6 provides combustion air removal in
the first stage heat exchanger and B15 serves the second
heat exchanger.
All combustion air blower motors are sealed and cannot be
oiled. The blower cannot be adjusted but can be disas
sembled for cleaning.
TABLE 3
COMBUSTION AIR BLOWER
Unit Misc.
Requires T3
When used on
460v or 575v units
GCS16823Y
GCS16953Y
Wheel (in.)
4.5 x 1.25
Electrical
208/230v/
1ph/60Hz.
PSC
GCS16823G,J
GCS16953G,J
4.5 x 1.25
460v/
1ph/60Hz.
PSC
Requires T3
When used on
460v or 575v units
GCS161353Y
GCS161603Y
GCS161853235Y,G,J
4.81 x 1.25
208/230v/
1ph/60Hz.
PSC
GCS161353G,J
GCS161603G,J
4.81 x 1.25
460v/
1ph/60Hz.
PSC
GCS161853330Y,G,J
GCS162553235Y,G,J
GCS162753235Y,G,J
GCS163003235Y,G,J
GCS162553470Y,G,J
GCS162753470Y,G,J
GCS163003470Y,G,J
5.33 x 1.50
208/230v/
1ph/60 Hz.
PSC
Requires T3
When used on
460v or 575v units
Requires T3
When used on
575v units
Requires T3
When used on
575v units
The combustion air blower uses a singlephase PSC mo
tor which requires a run capacitor (C3). All motors operate
at 3200RPM. All have automatic reset overload protec
tion. Blowers are supplied by various manufacturers.
Combustion Air Blower Ratings may vary by manufactur
er. Specific blower electrical ratings can be found on the
unit rating plate. Table 3 shows other important specifica
tions.
Combustion air blower B15 is only used in units equipped
with dual heat exchangers. B15 is identical to B6. B15 pro
vides combustion air removal in the second stage heat ex
changer.
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