Gas Pressure Measurement - Lennox ELITE Series 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
operation. Switch is factory-set and requires no
adjustment.
3 - After a 15-second prepurge, the hot surface ignitor
energizes.
4 - After a 20-second ignitor warm-up period, the gas
valve solenoid opens. A 4-second Trial for Ignition
period 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
ignition 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 automatically 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
TABLE 24
GAS METER CLOCKING CHART
Seconds for One Revolution
EL296
Natural
Unit
1 cu ft
Dial
-045 80
-070 55
-090 41
-110 33
Natural-1000 btu/cu ft LP-2500 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
110 136
82 102
66 82
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 24. If manifold pressure matches TABLE 26 and
rate is incorrect, check gas orifices for proper size and
restriction. Remove temporary gas meter if installed.
Supply Pressure Measurement
An inlet pressure post located on the gas valve provides
access to the supply pressure. See FIGURE 61. Back out
the 3/32 hex screw one turn, connect a piece of 5/16 tub-
ing and connect to a manometer to measure supply pres-
sure. See TABLE 26 for supply line pressure.
Manifold Pressure Measurement
A manifold pressure post located on the gas valve pro-
vides access to the manifold pressure. See FIGURE 61.
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.
To correctly measure manifold pressure, the differential
pressure between the positive gas manifold and the neg-
ative 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 26.
5 - If necessary, make adjustments. FIGURE 61 shows
location of high fire and low fire adjustment screws.
6 - Repeat steps 3, 4 and 5 on high fire. See values in
TABLE 26.
7 - Shut unit off and remove manometer as soon as an
accurate 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.
400
272
204
164
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