Lennox SL280DFNV Series Unit Information page 30

TABLE 18
Manifold and Pressure Signal wc. Natural
Manifold
Altitude Unit
High
Fire
-060
0-4500ft 3.0-3.8
-080
-060
4500-
2.5-3.3
7500ft
-080
TABLE 19
Manifold and Pressure Signal wc. Propane
Manifold
Altitude Unit
High
Fire
-060
1
0-4500ft 3.4-3.8
-080
2
-060 2.7-3.2
4500- 1
7500ft
-080 N/A
1 Use Lp Kit 20P40
2 Use LP Kit 20P41 (0-4500ft only)
Air Orifice Replacement
Do not replace the air orifice until the problem has been
determined. If the unit has difficulty igniting the orifice is
oversized and brings in too much air. If the unit ignites
but with loud resonance the orifice is too small and needs
more air.
Inlet Screen
Signal
Low
High Fire Low Fire
Fire
0.77-0.85 0.34-0.42
1.3-1.7
0.78-0.86 0.35-0.43
1.3-1.7 0.60-0.85 0.30-0.45
Signal
Low
High Fire Low Fire
Fire
0.77-0.85 0.34-0.42
1.5-1.9
0.78-0.86 0.35-0.43
1.3-1.7 0.60-0.85 0.30-0.45
N/A N/A N/A
Air Orifice Replacement
Gray Coupling
4
7
8 2
7
The air orifice is located inside the gray coupling between
the clamps. FIGURE 19 shows corresponding steps with
the steps below.
1 - Turn off the electrical power and gas supply to the
furnace.
2 - Remove the air hose fitting from the brass fitting on
the air inlet screen.
3 - Use a 5/16" nut driver to loosen the clamps on the
gray coupling.
4 - Remove the air inlet screen housing and coupling.
5 - Remove the air orifice. Check the "Part" number
stamped on the air orifice. See TABLE 20. If
incorrect replace with proper air orifice. Repeat
manifold check. If air orifice is correct then it must
be replaced. See TABLE 20 for replacement.
6 - Reinstall the air orifice on the right side of the
coupling and push firmly into place.
7 - Reinstall air inlet housing and coupling making
sure the coupling is fully seated against the air inlet
elbow. Tighten clamps to secure the coupling.
8 - Reconnect the air pressure tubing.
9 - Repeat manifold and signal pressure check. If
unit ignites and manifold and signal pressure are
correct, move on to combustion check. If unit still
does not ignite or ignites with loud resonance go to
Troubleshooting FIGURE 21.
Part Number
5
6
3
FIGURE 19
Page 30