Proper Combustion - Lennox DAVE SIGNATURE SL280DFV Installation Instructions Manual

Failure To Operate
If the unit fails to operate, check the following:
1 - Is the thermostat calling for heat?
2 - Are access panels securely in place?
3 - Is the main disconnect switch closed?
4 - Is there a blown fuse or tripped circuit breaker?
5 - Is the filter dirty or plugged? Dirty or plugged filters
will cause the limit control to shut the unit off.
6 - Is gas turned on at the meter?
7 - Is the manual main shut-off valve open?
8 - Is the internal manual shut-off valve open?
9 - Is the unit ignition system in lock out? If the unit locks
out again, call the service technician to inspect the
unit for blockages.
10 - Is pressure switch closed? Obstructed flue will
cause unit to shut off at pressure switch. Check flue
and outlet for blockages.
11 - Is the rollout switch tripped? If the switch is tripped
call the service technician to inspect the unit.
Gas Pressure Adjustment
Gas Flow (Approximate)
Furnace should operate at least 5 minutes before check-
ing gas flow. Determine time in seconds for two revolu-
tions of gas through the meter. (Two revolutions assures
a more accurate time.) Divide by two and compare to time
in TABLE 19 below. If manifold pressure matches TABLE
21 and rate is incorrect, check gas orifices for proper size
and restriction. Remove temporary gas meter if installed.
NOTE - Shut unit off and remove manometer as soon as
an accurate reading has been obtained. Take care to re-
place pressure tap plug.
TABLE 19
GAS METERING CLOCKING CHART
Natural 1000 btu/cu ft
SL280
Seconds For One Revolution
Unit
1 cu ft dial 2 cu fr dial 1 cu ft Dial 2 cu ft Dial
-070 55
-090 41
-110 33
LP 2500 btu cu/cu ft
110 136 272
82 102 204
66 82 164
Supply Line Pressure
An inlet post located on the gas valve provides access to
the supply pressure. See FIGURE 24. Back out the 3/32
hex screw one turn, connect a piece of 5/16 tubing and
connect to a manometer to measure supply pressure. See
TABLE 21 for supply line pressure.
Manifold Pressure
NOTE - Pressure test adapter kit (10L34) is available from
Lennox to facilitate manifold pressure measurement.
A manifold pressure tap located on the gas valve provides
access to the manifold pressure. See FIGURE 24. Back
out the 3/32 hex screw one turn, connect a piece of 5/16
tubing and connect to a manometer to measure manifold
pressure.
1 - Connect the test gauge positive side "+" to manifold
pressure tap on gas valve as noted above.
2 - Ignite unit on low fire and let run for 5 minutes to
allow for steady state conditions.
3 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in
TABLE 21.
4 - If necessary, make adjustments. FIGURE 24 shows
location of high fire and low fire adjustment screws.
5 - Repeat steps 3, 4 and 5 on high fire. See values in
TABLE 21.
6 - Shut unit off and remove manometer as soon as
an accurate reading has been obtained. Turn the
supply and manifold 3/32" hex screws one revolution
back into the gas valve.
7 - Start unit and perform leak check. Seal leaks if
found.

Proper Combustion

Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking com-
bustion. Table 20 shows acceptable combustion for ALL
SL280DFV models.
Firing Rate
High Fire
Low Fire
The carbon monoxide reading should not exceed 100 ppm.
Page 39
TABLE 20
CO2% For Nat CO2% For L.P.
6.0 - 7.4 6.9 - 8.4
4.8 - 6.0 5.7 - 7.0