Lennox ML180DF045P24A - Gas Pressure Adjustment; Proper Combustion; High Altitude

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11 - Are ame rollout switches tripped? If ame rollout
switches are tripped, call the service technician for
inspection.
Heating Sequence Of Operation
1 - When thermostat calls for heat, combustion air
blower 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, ame sensor proves the ame, and
the combustion process continues.
6 - If ame is not detected after rst ignition trial,
the ignition control will repeat steps 3 and 4 four
more times before locking out the gas valve
(”WATCHGUARD” ame failure mode).The ignition
control will then automatically repeat steps 1
through 6 after a 60 minute.
7 - 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 9
GAS METER CLOCKING CHART
ML180
Unit
Seconds for One Revolution
Natural LP
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
Dial
-045 80 160 200 400
-070 55 110 136 272
-090 41 82 102 204
-110 33 66 82 164
-135 27 54 68 136
Natural-1000 btu/cu ft LP-2500 btu/cu ft
Furnace should operate at least 5 minutes before check-
ing gas ow. 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 9 below. If manifold pressure matches table 11 and
rate is incorrect, check gas orices for proper size and
restriction. Remove temporary gas meter if installed.
NOTE - To obtain accurate reading, shut off all other gas
appliances connected to meter.
Supply Pressure Measurement
A threaded plug on the inlet side of the gas valve provides
access to the supply pressure tap. Remove the threaded
plug, install a eld-provided barbed tting and connect a
manometer to measure supply pressure. Furnace should
operate at least 5 minutes before checking supply pres-
sure. See table 11 for proper supply pressure. Replace
the threaded plug after measurements have been taken
Manifold Pressure Measurement
1 - Remove the threaded plug from the outlet side of
the gas valve and install a eld-provided barbed
tting. Connect to a manometer to measure manifold
pressure.
2 - Start unit and allow 5 minutes for unit to reach
steady state.
3 - While waiting for the unit to stabilize, observe the
ame. Flame should be stable and should not lift
from burner. Natural gas should burn blue.
4 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in
table 11.
5 - Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to
replace pressure tap plug.
6 - Start unit and perform leak check. Seal leaks if
found.
Proper Combustion
Furnace should operate a minimum 15 minutes with cor-
rect manifold pressure and gas ow rate before checking
combustion. Take combustion sample beyond the ue out-
let and compare to the tables below. The maximum car-
bon monoxide reading should not exceed 100 ppm.
TABLE 10
ML180UH Unit CO2% For Nat CO2% For L.P.
-045
6.0 - 7.5 6.9 - 8.5
-070
-090
-110
High Altitude
The manifold pressure may require adjustment and com-
bustion air pressure switch may need replacing to ensure
proper combustion at higher altitudes. Refer to table 11
for manifold pressure and table 12 for pressure switch
change and gas conversion kits.
IMPORTANT
For safety, shut unit off and remove manometer as soon
as an accurate reading has been obtained. Take care to
replace pressure tap plug.