Gas Pressure Measurement; Gas Pressure Adjustment - Lennox EL296UHE 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 14
GAS METER CLOCKING CHART
Seconds for One Revolution
Natural
EL296
Unit 1 cu ft
Dial
-045 80
-070 55
-090 41
-110 33
-135 27
Natural-1000 btu/cu ft
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
54 68 136
LP-2500 btu/cu ft
Furnace should operate at least 5 minutes before checking
gas flow. Determine time in seconds for two revolutions of
gas through the meter. (Two revolutions assures a more
accurate time.) Divide by two and compare to time in table
14. If manifold pressure matches table 16 and rate is incor­
rect, check gas orifices for proper size and restriction. Re­
move temporary gas meter if installed.
NOTE - To obtain accurate reading, shut off all other gas
appliances connected to meter.
Supply Pressure Measurement
An inlet post located on the gas valve provides access to
the supply pressure. See figure 59. 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 16
for supply line pressure.
On multiple unit installations, each unit should be checked
separately, with and without units operating. Supply pres­
sure must fall within range listed in table 16.
Manifold Pressure Measurement
NOTE - Pressure test adapter kit (10L34) is available from
Lennox to facilitate manifold pressure measurement.
A manifold pressure post located on the gas valve provides
access to the manifold pressure. See figure 59. 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.
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 con­
nect 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
16.
5 - If necessary, make adjustments. Figure 59 shows
location of high fire and low fire adjustment screws.
6 - Repeat steps 3, 4 and 5 on high fire. See values in
table 16.
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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