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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 30. S47 is wired to the A55 Unit
Controller. When S47 senses flame roll-out (indicating a
blockage in the combustion air passages), the flame
roll-out limit trips and the ignition control immediately
closes 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 30 for location. Switch S18 is
wired to the A55 Unit Controller.
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 30 for the inducer location. The inducer is ener
gized by the A55 Unit Controller via K13 relay.
The inducer uses a 208/230V single‐phase PSC motor and a
4.81in. x 1.25in. (122mm x 32mm) blower wheel. The motor
operates at 3200RPM and is equipped with auto‐reset over
load protection. Blower is supplied by various manufacturers.
Ratings may vary by manufacturer. Specific blower electrical
ratings can be found on the unit rating plate.
All combustion air blower motors are sealed and cannot
be oiled. The blower cannot be adjusted but can be dis
assembled for cleaning.
9-Combustion Air Motor Capacitor C3
Combustion air inducer B6 requires a run capacitor rat
ed 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 A55. 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 provid
ed on the valve for shut-off. Manual shut‐off knob immedi
ately closes both stages without delay. Figure 31 shows
gas valve components. Table 4 shows factory gas valve
regulation for LGH units.
HEATING SECTION COMPONENTS
FIGURE 30
IGNITION
WIRE
J15 P15
J29
B6
COMBUSTION
AIR INDUCER
GV1 GAS
VALVE
S18 BLOWER
PROVING SWITCH
S10
PRIMARY
LIMIT
SWITCH
A3
IGNITION
CONTROL
SENSOR
WIRE
J19
P19
S47 ROLLOUT
SWITCH
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