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6-Flame Roll-out Limit S47
Flame roll-out limit S47 is a SPST N.C. high temperature
limit located as shown in figure 15. S47 is wired to the A3
ignition controller. When S47 senses flame roll-out (indicat
ing a blockage in the combustion air passages), the flame
roll-out limit trips and the ignition control immediately clos
es the gas valve.
Limit S47 in standard heat units is factory preset to open at
250_F +
12_F (121.1_C + 6.7_C) on a temperature rise. All
flame roll-out limits are manual reset.
7-Combustion Air Prove Switch S18
S18 is a SPST N.O. switch which monitors combustion air
inducer operation. See figure 15 for location. Switch S18 is
wired to the A3 ignition control.
The switch closes on a negative pressure fall. This negative
pressure fall and switch actuation allows the ignition se
quence to continue (proves, by closing, that the combus
tion air inducer is operating before allowing the gas valve to
open.) The combustion air prove switch is factory set and
not adjustable. The switch will automatically open on a
pressure rise (less negative pressure). S18 closes at 0.25 +
5 in.w.c. (62.3 + 12.4 Pa) and opens at 0.10 + 5 in.w.c. (24.8
+
12.4Pa)
8-Combustion Air Inducer B6
The combustion air inducer provides fresh air to the burner
while clearing the combustion chamber of exhaust gases.
See figure 15 for the inducer location. The inducer is ener
gized by the A3 ignition control via an on board mounted re
lay.
The inducer uses a 208/230V single‐phase PSC motor and
a 4.81in. x 1.25in. (122mm x 32mm) blower wheel. The mo
tor operates at 3200RPM and is equipped with auto‐reset
overload protection. Blower is supplied by various manu
facturers. Ratings may vary by manufacturer. Specific
blower electrical ratings can be found on the unit rating
plate. Unit with main voltage of 460VAC (G) will use a
460VAC Combustion Air Inducer B6. 240VAC (Y) and
575VAC (J) use a 230V Combustion Air Inducer
All combustion air blower motors are sealed and cannot be
oiled. The blower cannot be adjusted but can be disassem
bled for cleaning.
9-Combustion Air Motor Capacitor C3
Combustion air inducer B6 requires a run capacitor rated at
3 MFD and 370VAC.
10-Gas Valves GV1
Gas valve GV1 is a two‐stage redundant valve. Units are
equipped with valves manufactured by White-Rodgers or
Honeywell. On both valves first stage (low fire) is quick
opening (on and off in less than 3 seconds). On the White-
Rodgers valve second stage is slow opening (on to high fire
pressure in 40 seconds and off to low fire pressure in 30
seconds). On the Honeywell second stage is quick open
ing. On a call for first stage heat (low fire), the valve is ener
gized by the ignition control simultaneously with the spark
electrode. On a call for second stage heat (high fire), the
second stage operator is energized directly from A3 ignition
controller. The White-Rodgers valve is adjustable for high
fire only. Low fire is not adjustable. The Honeywell valve is
adjustable for both low fire and high fire. A manual shut-off
knob is provided on the valve for shut-off. Manual shut‐off
knob immediately closes both stages without delay. Figure
24 shows gas valve components. Table 10 shows factory
gas valve regulation for LGM units.
GAS VALVE REGULATION FOR LGM UNITS
Maximum
Inlet
Pressure
Operating Pressure
(outlet) Factory Setting
13.0”W.C.
3232Pa
Natural
L.P
.
3.7+0.3”W.C.
920+75Pa
Low High Low High
1.6+0.2”W.C.
398+50Pa
10.5+0.5”W.C.
2611+7124Pa
5.5+0.3”W.C.
1368+75Pa
TABLE 10
FIGURE 24
WHITE RODGERS 36H54 GAS VALVE
Two-Stage
LOW FIRE
ADJUSTMENT
HIGH FIRE
ADJUSTMENT
INLET
PRESSURE
TAP
MANIFOLD
PRESSURE
TAP
GAS VALVE SWITCH SHOWN IN ON POSITION.
HONEYWELL VR8205Q/VR8305Q GAS VALVE
GAS VALVE KNOB IS SHOWN IN OFF POSITION.
LOW FIRE
ADJUSTMENT
HIGH FIRE
ADJUSTMENT
INLET
PRESSURE
TAP
MANIFOLD
PRESSURE
TAP
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