Heating System Service Checks; Csa Certification; Testing Gas Piping; Testing Gas Supply Pressure - Lennox ML296UHV(X) Series Manual

IV-HEATING SYSTEM SERVICE CHECKS
A-CSA Certification
All units are CSA design certified without modifications.
Refer to the ML296UHV(X) Installation Instruction.
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.
WARNING
Do not exceed 600 in-lbs (50 ft-lbs) torque 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 dis­
connected and isolated. Gas valves can be damaged if
subjected to more than 0.5 psig (14" W.C.). See figure 50. 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.
GAS PIPING TEST PROCEDURE
MANUAL MAIN SHUT-OFF VALVE
WILL NOT HOLD TEST PRESSURE
IN EXCESS OF 0.5 PSIG (14"W.C.)
GAS VALVE
FIGURE 50
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
1/8 NPT PLUG
CAP
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
An inlet pressure post located on the gas valve provides ac­
cess to the supply pressure. See figure 49. 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 21 for supply line pressure.
E-Check Manifold Pressure
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 49. 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.
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.
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 connect
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 low
fire manifold pressure and compare to value given in
table 21. If necessary, make adjustment. Figure 49
shows location of low fire adjustment screw.
5 - Repeat on high fire and compare to value given in
table 21. If necessary, make adjustment. Figure 49
shows location of high fire adjustment screw.
6 - Shut unit off and remove manometer as soon as an ac­
curate reading has been obtained.
7 - Start unit and perform leak check. Seal leaks if found.
The gas valve is factory set and should not require adjust­
ment. All gas valves are factory regulated.
F- 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 18 below. If manifold pressure matches table 21
and rate is incorrect, check gas orifices for proper size and
restriction.
Page 44