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Gas supply piping should not allow more than 0.5”W.C. drop
in pressure between gas meter and unit. Supply gas pipe
must not be smaller than unit gas connection.
Compounds used on gas piping threaded joints should be
resistant to action of liquefied petroleum gases.
C-Testing Gas Piping
IMPORTANT
In case emergency shutdown is required, turn off
the main shut‐off valve and disconnect the main
power to unit. These controls should be properly
labeled by the installer.
When pressure testing gas lines, the gas valve must be dis
connected and isolated. Gas valves can be damaged if
subjected to more than 0.5 psig (14” W.C.). See figure 18
.
If
the pressure is greater than 0.5psig (14”W.C.), use the
manual shut-off valve before pressure testing to isolate fur
nace from gas supply.
FIGURE 18
MANUAL MAIN SHUT-OFF VALVE
WILL NOT HOLD TEST PRESSURE
IN EXCESS OF 0.5 PSIG (14”W.C.)
GAS VALVE
CAP
GAS PIPING TEST PROCEDURE
1/8 NPT PLUG
When checking piping connections for gas leaks, use pre
ferred means. Kitchen detergents can cause harmful corro
sion 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-Testing Gas Supply Pressure
A port on the inlet side of the gas valve provides access to
the supply pressure tap. See figure 17. Loosen the screw
and connect a manometer to measure supply pressure.
The minimum supply line pressure is 4.5” - 13.0”w.c. For
natural and 11.0 - 13.0” wc for LP/Propane. Tighten after
measurements have been taken.
IMPORTANT
For safety, connect a shut‐off valve between the ma
nometer and the gas tap to permit shut off of gas
pressure to the manometer.
E- Proper Gas Flow (Approximate)
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 17 below.
NOTE- To obtain accurate reading, shut off all other gas
appliances connected to meter.
TABLE 17
GAS METER CLOCKING CHART
SL280N
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
-70
55
110
136
272
-90
41
82
102
204
-110
33
66
82
164
-135
27
54
68
136
Natural-1000 btu/cu ft LP-2500 btu/cu ft
F-Check Manifold Pressure
Manifold and Signal Pressure Check
1 - Turn off the electrical power and gas supply to the fur
nace.
2 - Remove the threaded plug from the outlet side of the
gas valve and install a field-provided barbed fitting.
Connect measuring device positive “+” to barbed fit
ting to measure manifold pressure. See figure 17 for
manifold location.
3 - Install hoses and meter as shown in figure 20 for signal
pressure measurement.
4 - After allowing unit to stabilize for
8 minutes
, record
manifold pressure and compare to value in table 18 or
table 19. If manifold pressure is within range, rate
check is complete move to step 6. If manifold pressure
is not within range continue.
Valve is not adjustable. Do not adjust manifold
pressure.
5 - Record signal pressure and compare to value in table
18 or table 19. If signal pressure is within range contin
ue. If the signal is not within range go to “Troubleshoot
ing”.
6 - Shut off unit and remove manometer and signal meter
after accurate readings has been obtained.
7 - Restart unit and check for gas leaks. Seal any leaks
found.
If the unit has difficulty igniting or ignites with loud res
onance the air orifice must be checked and replaced if
necessary.
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.
