Gas Pressure Measurement; Gas Pressure Adjustment - Lennox EL296DFV Installation Instructions Manual

4 - Move gas valve switch to OFF.
5 - Replace the access panel.
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 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 lockout? If the unit locks out
again, inspect the unit for blockages.
Heating Sequence Of Operation
1 - When thermostat calls for heat, combustion air inducer
starts.
2 - Combustion air pressure switch proves blower opera­
tion. Switch is factory-set and requires no adjustment.
3 - After a 15-second prepurge, the hot surface ignitor en­
ergizes.
4 - After a 20-second ignitor warm-up period, the gas
valve solenoid opens. A 4-second Trial for Ignition peri­
od begins."
5 - Gas is ignited, flame sensor proves the flame, and the
combustion process continues.
6 - If flame is not detected after first ignition trial, the igni­
tion control will repeat steps 3 and 4 four more times
before locking out the gas valve ("WATCHGUARD"
flame failure mode). The ignition control will then auto­
matically repeat steps 1 through 6 after 60 minutes.
To interrupt the 60-minute "WATCHGUARD" period,
move thermostat from "Heat" to "OFF" then back to
"Heat". Heating sequence then restarts at step 1.

Gas Pressure Adjustment

Gas Flow (Approximate)
TABLE 22
GAS METER CLOCKING CHART
Seconds for One Revolution
Natural
EL296
Unit
1 cu ft
Dial
-045 80
-070 55
-090 41
-110 33
Natural-1000 btu/cu ft
NOTE - To obtain accurate reading, shut off all other gas
appliances connected to meter.
LP
2 cu ft 1 cu ft 2 cu ft
Dial Dial DIAL
160 200 400
110 136 272
82 102 204
66 82 164
LP-2500 btu/cu ft
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 22. If manifold pressure matches table 24 and rate
is incorrect, check gas orifices for proper size and restric­
tion. Remove temporary gas meter if installed.
Supply Pressure Measurement
An inlet pressure post located on the gas valve provides ac­
cess to the supply pressure. See figure 60. 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 24 for supply line pressure.
Manifold Pressure Measurement
A manifold pressure post located on the gas valve provides
access to the manifold pressure. See figure 60. Back out
the 3/32 hex screw one turn, connect a piece of 5/16 tubing
and connect to a manometer to measure manifold pres­
sure.
To correctly measure manifold pressure, the differential
pressure between the positive gas manifold and the nega­
tive burner box must be considered.
NOTE - Pressure test adapter kit (10L34) is available from
Lennox to facilitate manifold pressure measurement.
1 - Connect the test gauge positive side "+" to manifold
pressure tap on gas valve as noted above.
2 - Tee into the gas valve regulator vent hose and connect
to test gauge negative "-".
3 - Ignite unit on low fire and let run for 5 minutes to allow
for steady state conditions.
4 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
24.
5 - If necessary, make adjustments. Figure 60 shows
location of high fire and low fire adjustment screws.
6 - Repeat steps 3, 4 and 5 on high fire. See values in
table 24.
7 - Shut unit off and remove manometer as soon as an ac­
curate reading has been obtained. Turn the supply
and manifold 3/32" hex screw one revolution back into
the gas valve.
8 - Start unit and perform leak check. Seal leaks if found.
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