Page 20
MANUAL MAIN
SHUT-OFF VALVE
WILL NOT HOLD
NORMAL TEST
PRESSURE
CAP
ISOLATE
GAS VALVE
FURNACE
1/8 NPT PLUG
FIGURE 19
When checking piping connections for gas leaks, use
preferred means. Kitchen detergents can cause harmful
corrosion on various metals used in gas piping. Use of a
specialty Gas Leak Detector is strongly recommended. It
is available through Lennox under part number 31B2001.
See Corp. 8411-L10, for further details.
Do not use matches, candles, flame or any other source of
ignition to check for gas leaks.
D- Gas Pressure Adjustment
Gas Flow (Approximate)
TABLE 10
GAS METER CLOCKING CHART
Unit
Seconds For One Revolution
Natuarl
LP/Propane
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 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 10. If manifold pressure matches table 12 and rate is
incorrect, check gas orifices 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.
E- Supply and Manifold Pressure
Supply Pressure Measurement
1 -
Remove the threaded plug from the inlet side of
the gas valve and install a field-provided barbed
fitting. Connect to a test gauge to measure supply
pressure.
2 -
Start unit and allow 5 minutes for unit to reach
steady state.
3 - After allowing unit to stabilize for 5 minutes, record
supply pressure and compare to value given in
table 12.
Manifold Pressure Measurement
1 -
Remove the threaded plug from the outlet side of
the gas valve and install a field-provided barbed
fitting. Connect to a test gauge 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
flame. 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 12.
NOTE -
Shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to remove barbed fitting and replace
threaded plug.
F- Proper Combustion
Furnace should operate a minimum 15 minutes with cor
-
rect manifold pressure and gas flow rate before checking
combustion. Take combustion sample beyond the flue out
-
let and compare to the table below.
The maximum car-
bon monoxide reading should not exceed 100 ppm.
TABLE 11
ML180DFE Unit
CO
2
% Nat
CO
2
% LP
-045
6.8 - 7.4
7.5 - 9.0
-070
-090
-110
G- 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 12
for manifold pressure and table 13 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
.
