Heating System Service Checks - Lennox SL297UHNV Series Unit Information

IV-HEATING SYSTEM SERVICE CHECKS
A-C.S.A. Certification
All units are C.S.A. design certified without modifications.
Refer to the SL297UHNV Operation and Installation In-
struction Manual Information.
B-Gas Piping
CAUTION
If a flexible gas connector is required or allowed by
the authority that has jurisdiction, black iron pipe
shall be installed at the gas valve and extend outside
the furnace cabinet. The flexible connector can then
be added between the black iron pipe and the gas
supply line.
WARNING
Do not over torque (800 in-lbs) or under torque (350
in-lbs) when attaching the gas piping to the gas
valve.
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
disconnected and isolated. Gas valves can be damaged if
subjected to more than 0.5 psig (14" W.C.). See FIGURE
45. Ifthe pressure is greater than 0.5psig (14"W.C.), use
the manual shut-off valve before pressure testing to iso-
late furnace from gas supply.
Isolate Gas Valve
FIGURE 45
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.
Manual Main Shut-Off Valve Will
Not Hold Normal Test Pressure
1/8" N.P.T.
Plugged Tap
Cap
Do not use matches, candles, flame or any other
source of ignition to check for gas leaks.
D-Testing Gas Supply Pressure
A threaded plug on the inlet side of the gas valve provides
access to the supply pressure tap. Remove the threaded
plug, install a field-provided barbed fitting and connect a
manometer to measure supply pressure. The minimum
supply line pressure is 4.5" - 10.50"w.c. for natural and
11.0 - 13.0" wc for LP/Propane. Replace the threaded plug
after measurements have been taken.
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 25 below. If manifold pressure matches table 25
and rate is incorrect, check gas orifices for proper size and
restriction.
NOTE- To obtain accurate reading, shut off all other gas
appliances connected to meter.
GAS METER CLOCKING CHART
EL195E
Model
-040
-060
-080
Natural-1000 btu/cu ft / Propane 2500 btu/cu ft
F- Manifold and Signal Pressure Measurement
To correctly measure manifold and signal pressure, follow
the steps below:
1 - Turn off the electrical power and gas supply to the
furnace.
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 fitting to measure manifold pressure. See
FIGURE 44 for manifold location.
3 - Install hoses and meter as shown in figure 48 for
signal pressure measurement.
4 - Start unit on low fire and after allowing unit to
stabilize for 8 minutes, record manifold pressure
and compare to value in table 27. Repeat on high
fire. 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.
Page 53
WARNING
TABLE 25
Seconds For One Revolution
LP/Propanae
Natural
1 cu ft 2 cu ft 1 cu ft
Dial Dial Dial
90 180 n/a
60 120 150
45 90 112
2 cu ft
Dial
n/a
300
224