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IV-HEATING SYSTEM SERVICE CHECKS
A-C.S.A. Certification
All units are C.S.A. design certified without modifications.
Refer to the ML193UHE Operation and Installation In
-
struction Manual Information.
B-Gas Piping
IMPORTANT
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.
CAUTION
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. Com
-
pounds used on gas piping threaded joints should be re
-
sistant 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 0.5psig (14” W.C.). See FIGURE
55.
MANUAL MAIN SHUT-OFF
VALVE WILL NOT HOLD
NORMAL TEST PRESSURE
CAP
FURNACE
ISOLATE
GAS VALVE
1/8” N.P.T. PLUGGED TAP
FIGURE 55
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.
WARNING
Do not use matches, candles, flame or any other
source of ignition to check for gas leaks.
D-Testing Gas Supply Pressure Gas Flow
(Approximate)
TABLE 17
GAS METER CLOCKING CHART
ML193
Unit
Seconds for One Revolution
Natural
LP
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
Dial
-030
120
240
300
600
-045
80
160
200
400
-070
55
110
136
272
-090
41
82
102
204
-110
33
66
82
164
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 17. If manifold pressure matches TABLE 19 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.
Supply Pressure Measurement
When testing supply gas pressure, use the 1/8” N.P.T.
plugged tap or pressure post located on the gas valve to
facilitate test gauge connection. See FIGURE 54. Check
gas line pressure with unit firing at maximum rate. Low
pressure may result in erratic operation or underfire. High
pressure can result in permanent damage to gas valve or
overfire.
On multiple unit installations, each unit should be checked
separately, with and without units operating. Supply pres
-
sure must fall within range listed in TABLE 19.
