Lennox SL280UHNV Series Unit Information page 33

TABLE 18
Manifold and Pressure Signal wc. Natural
Manifold
Unit
High Fire Low Fire
060
080
3.0 - 3.8 1.3 - 1.7
100
TABLE 19
Manifold and Pressure Signal wc. Propane
Manifold
Unit
High Fire Low Fire
1
060
3.4-3.8 1.5-1.9
2
080
100 N/A
1 Use LP Kit 20P40
2 Use LP Kit 20P41
Air Orifice Replacement
Do not replace the air orifice until the problem has been de­
termined. If the unit has difficulty igniting the orifice is over­
sized and brings in too much air. If the unit ignites but with
loud resonance the orifice is too small and needs more air.
The air orifice is located inside the gray coupling between
the clamps. Figure 19 show corresponding steps with the
steps below.
Inlet Screen
Signal
High Fire Low Fire
0.77-0.85 0.34-0.42
078-0.86 0.35-0.43
0.62-0.70 0.29-0.37
Signal
High Fire Low Fire
0.77-0.85 0.34-0.42
078-0.86 0.35-0.43
N/A N/A N/A
Air Orifice Replacement
Gray Coupling
4
7
8 2
3
7
1 - Turn off the electrical power and gas supply to the fur­
nace.
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 re­
place 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 ig­
nites and manifold and signal pressure are correct,
move on to combustion check. If unit still does not ig­
nite or ignites with loud resonance go to Troubleshoot­
ing figure 21.
Part Number
5
6
FIGURE 19
Page 33