Page 32
5-Flame Rollout Limits S47, S69
second heat section are SPST N.C. high temperature
limits located just above the burner air intake opening in
the ignition control immediately closes the gas valve. Limit
rise, while on high heat units both limits open at 270 F +
-
out limits are manual reset.
6-Combustion Air Prove Switches S18, S45
heat section) are located below the compressors. Each
has its own control box. Both are identical SPST N.O.
switches and monitor combustion air inducer operation.
Switch S18 and S45 are wired to the A55 Unit Controller.
The switch closes on a negative pressure fall. This nega-
tive pressure fall and switch actuation allows the ignition
sequence to continue (proves, by closing, that the com-
bustion 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). Table 7 shows
prove switch settings.
TABLE 7
S18 & S45 Prove Switch Settings
Close“ w.c. (Pa) Open “ w.c. (Pa)
0.10+5 (24.8+12.4)
7-Combustion Air Inducers B6 & B15
B15 on the second heat section, are identical blowers
which provide fresh air to the corresponding burners while
clearing the combustion chamber of exhaust gases. The
blowers begin operating immediately upon receiving a
thermostat demand and are de-energized immediately
-
glephase PSC motor and a 4.81in. x 1.25in. (122mm x
32mm) blower wheel. All motors operate at 3200 or 3450
RPM and are equipped with auto-reset overload protec-
tion. Blowers are supplied by various manufacturers. Rat-
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 disas-
sembled for cleaning.
8-Combustion Air Motor Capacitors C3 & C11
The combustion air blower motors in all LGM units re-
quire run capacitors. Capacitor C3 is connected to com-
-
tion air blower B15. Both capacitors are rated at 3 or 4
Valves GV1 & GV3 Gas valves GV1 and GV3 are identi-
cal. The gas valves are two-stage redundant valves. Units
are equipped with valves manufactured by Honeywell.
stage is quick opening.
-
gized by the ignition control simultaneously with the spark
second stage operator is energized directly from A55
(GV1, GV3). The Honeywell valve is adjustable for both
-
ly closes both stages without delay. Figure 22 shows gas
valve components.
Table 8 shows factory gas valve regulation for LGM series
units. Optional factory installed gas valves for single stage
valves are wired without W2 eliminating two stage heat.
LOW FIRE
ADJUSTMENT
HIGH FIRE
ADJUSTMENT
INLET
PRESSURE
TAP
MANIFOLD
PRESSURE
TAP
GAS VALVE
GAS VALVE SHOWN IN “OFF” POSITION
FIGURE 22
TABLE 8
GAS VALVE REGULATION FOR LGM UNITS
Operating Pressure (outlet) Factory Setting
Natural LP
Low High Low High
3.7+0.3”WC
5.5+0.3”WC
10.5+0.5”WC
The maximum inlet pressure is 13.0” WC (3232PA)
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