Iv-Heating System Service Checks - Lennox ML193UH045P36B 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 ML193UH Operation and Installation Instruc­
tion 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.
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 0.5psig (14" W.C.). See figure 55.
MANUAL MAIN SHUT-OFF
VALVE WILL NOT HOLD
NORMAL TEST PRESSURE
1/8" N.P.T. PLUGGED TA­
P
CAP
FIGURE 55
When checking piping connections for gas leaks, use pre­
ferred means. Kitchen detergents can cause harmful cor­
rosion on various metals used in gas piping. Use of a spe­
cialty 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)
Furnace should operate at least 5 minutes before checking
gas flow. Determine time in seconds for two revolutions 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 20 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 pres­
sure may result in erratic operation or underfire. High pres­
sure can result in permanent damage to gas valve or over­
fire.
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 20.
Manifold Pressure Measurement
FURNACE
1 - Remove the threaded plug from the outlet side of the
ISOLATE
GAS VALVE
2 - Start unit and allow 5 minutes for unit to reach steady
3 - While waiting for the unit to stabilize, observe the
4 - After allowing unit to stabilize for 5 minutes, record
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.
E-Proper Combustion
Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking com­
bustion. Take combustion sample beyond the flue outlet
and compare to table 19.
Page 41
TABLE 18
GAS METER CLOCKING CHART
Seconds for One Revolution
Natural
ML193
Unit
1 cu ft 2 cu ft
Dial Dial
-045 80 160
-070 55 110
-090 41 82
-110 33 66
-135 27 54
Natural-1000 btu/cu ft
gas valve and install a field-provided barbed fitting.
Connect to a manometer to measure manifold pres­
sure.
state.
flame. Flame should be stable and should not lift from
burner. Natural gas should burn blue.
manifold pressure and compare to value given in table
20.
LP
1 cu ft 2 cu ft
Dial DIAL
200 400
136 272
102 204
82 164
68 136
LP-2500 btu/cu ft