Lennox SL280UHNV - Page 38

Page 38
Gas Manifold and System Operating Pressure Check
-05 Models With SIT Gas Valve
1 - Turn o󰀨 the electrical power and gas supply to the
furnace.
2 - Check the gas manifold pressure on the SIT gas
valve by opening the manifold pressure post. See
gure 18. Using a 4.5-5 x 0.8 mm screw driver,
loosen the slot headed brass sealing screws. The
sealant screws can not be removed.
3 - Install hoses and meter as shown in gures 24 and
25 for system operating pressure measurement.
The system operating pressure is monitored by the
pressure switch and is the pressure drop across the
air orice.
4 - Turn on electrical power and gas supply to the
furnace. Start Furnace.
5 - After allowing unit to stabilize for 8 minutes, record
manifold pressure and compare to value in table 23.
If manifold pressure is within range, rate check is
complete move to step 6. If manifold pressure is not
within range replace gas valve.
Gas Valve is not adjustable. Do not adjust
manifold pressure.
6 - Record system operating pressure and compare
to value in table 24. If system operating pressure
is within range continue. If the system operating
pressure is not within range go to “Troubleshooting”
gure 26.
7 - Shut o󰀨 unit and remove manometer and signal
meter after accurate readings has been obtained.
Remove measurement hoses. Tighten the brass
sealing screws loosened in step 2. Sealant screws
must be tightened before ring the unit.
8 - Restart unit and check for gas leaks. Seal any leaks
found.
If the unit has di󰀩culty igniting or ignites with loud
resonance see “Air Orice Replacement” and “Trou-
bleshooting” gure 26.
TABLE 23
Gas Manifold Pressure
Capacity
Gas Manifold Pressure
(in. w.c.)
Two-Stage Models Low Fire High Fire
060
0.0 - 0.10 0.0 - 0.10080
100
TABLE 24
System Operating Pressures (in.w.c.) at Di󰀨erent Altitudes
Capacity
System Operating Pressure at
0 - 500ft
System Operating Pressure at
500ft - 4500ft
System Operating Pressure at
4500ft - 7500ft
Two-Stage
Models
Low Fire High Fire Low Fire High Fire Low Fire High Fire
060 0.49 - 0.62 1.15 - 1.36 0.45 - 0.58 1.08 - 1.29 0.41 - 0.54 0.96 - 1.17
080 0.43 - 0.56 1.12 - 1.26 0.39 - 0.52 1.04 - 1.18 0.34 - 0.47 0.94 - 1.08
100 0.48 - 0.62 1.11 - 1.31 0.48 - 0.62 1.09 - 1.29 0.48 - 0.62 0.95 - 1.15