Lennox LDT Series Information page 30

The switch closes on a negative pressure fall. This negative
pressure fall and switch actuation allows the ignition
sequence to continue (proves, by closing, that the
combustion 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 6 shows
prove switch settings.
TABLE 6
S18 & S45 Prove Switch Settings
Close" w.c. (Pa)
0.25 + 5
(62.3+12.4)
7-Combustion Air Inducers B6 & B15
Combustion air blowers B6 on the first heat section and 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
when thermostat demand is satisfied.
Both combustion air blowers use a 208/230 or 460V
single‐phase 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 protection.
Blowers are 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
disassembled for cleaning.
8-Combustion Air Motor Capacitors
C3 & C11
The combustion air blower motors in all LDT units require
run capacitors. Capacitor C3 is connected to combustion
air blower B6 and C11 is connected to combustion air
blower B15. Capacitors are rated at 208/230V CAB has
4uF 450V capacitors 460V CAB has 2uF 450V capacito3 or
4 MFD for 208/230 CAB
9-Gas Valves GV1 & GV3
Gas valves GV1 and GV3 are identical. The gas valves are
two‐stage redundant valves. On both valves first stage (low
fire) is quick opening (on and off in less than 3 seconds). On
a call for first stage heat (low fire), the valve is energized 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 (GV1, GV3). The
valve is adjustable for both low fire and high fire. A manual
shut-off knob is provided on the valve for shut-off. Manual
Open " w.c. (Pa)
0.10+5
(24.8+12.4)
Page 30
shut‐off knob immediately closes both stages without
delay. Figure 24 shows gas valve components. Table 7
shows factory gas valve regulation for LDT series units.
Optional factory installed gas valves for single stage heat
only, are available for the LDT156, 180 and 240. Gas
valves are wired without W2 eliminating two stage heat.
WHITE RODGERS 36H54 GAS VALVE
Two-Stage
Outlet Pressure
Tap
Low Fire Adjustment
(under cap)
High Fire Adjustment
(under cap)
GAS VALVE SWITCH SHOWN IN ON POSITION.
FIGURE 24
TABLE 7
GAS VALVE REGULATION FOR LDT UNITS
Operating Pressure
Maximum (outlet) Factory Setting
Inlet
Natural
Pressure
Low
13.0"W.C. 1.6+0.2"W.C. 3.7+0.3"W.C.
3232Pa 398+50Pa 920+75Pa
10-Spark Electrodes
An electrode assembly is used for ignition spark. Two
identical electrodes are used (one for each gas heat
section). The electrode is mounted through holes on the
left‐most end of the burner support. The electrode tip
protrudes into the flame envelope of the adjacent burner.
The electrode assembly 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
(figure 25) and ignites the left 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 uses 1/4" (6.35 mm)female quick connect on the
electrode end and female spark plug-type terminal on the
ignition control end.
NOTE- IN ORDER TO MAXIMIZE SPARK ENERGY
TO ELECTRODE, HIGH VOLTAGE WIRE SHOULD
TOUCH UNIT CABINET AS LITTLE AS POSSIBLE.
Inlet Pressure Tap
L.P
.
High Low High
5.5+0.3"W.C. 10.5+0.5"W.C.
1368+75Pa 2611+7124Pa