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3. Gas Valve
The valve (figure 44) is internally redundant to assure safe
ty shut-off. If the gas valve must be replaced, the same type
valve must be used.
24VAC terminals and gas control knob are located on the
valve. A wire harness connects the terminals from the gas
valve to the electronic ignition control. 24V applied to the termi
nals energizes the valve.
Inlet and outlet pressure taps are located on the valve. A regu
lator adjustment screw is located on the valve.
4. Flame Rollout Switch (S47)
Flame rollout switch is a high temperature limit located on
the front of the intake air assembly.ner box, one on each
side.- See figure 13. The limit is a N.C. SPST auto-reset
limit. When S47 senses rollout, the circuit breaks and the
ignition control immediately stops ignition and closes the
gas valve. Rollout can be caused by a blocked heat ex
changer, flue or lack of combustion air.
5. Burner and Orifice
Burners are factory set and require no adjustment. Always
operate the unit with air gas plenum in place. The burner has
one orifice located between the gas valve and the air intake
assembly (figure13). To check or replace the orifice remove
the black iron inlet pipe from the gas valve then remove the
four screws securing the gas valve to the intake air pipe. The
orifice is located in the orifice housing. The burner uses an
orifice (see table 16) that is precisely matched to the burner
input. The burner can be removed for service. If burner has
been removed, it is critical to replace all gaskets.
TABLE 16
Nat Orifice Size
Unit Input
Orifice Size (0 - 4500 ft)
040
0.0472
060
0.0595
080
0.0689
6. Primary Limit Control (S10)
The primary limit (S10) is located in the heating vestibule pan
el. When excess heat is sensed in the heat exchanger, the
limit will open. If the limit is open, the furnace control energizes
the supply air blower and closes the gas valve. The limit auto
matically resets when unit temperature returns to normal. The
switch must reset within three minutes or the SureLight control
will go into Watch guard for one hour. The switch is factory
set and cannot be adjusted. The switch may have a different
set point for each unit model number. See Lennox Repair
Parts Handbook if limit switch must be replaced,
