System Service Checks; Heating System Service Checks - Lennox LGA Series Unit Information

IV− SYSTEMS SERVICE CHECKS
A−LGA/LGC Heating System Service Checks
All LGA/LGC units are A.G.A and C.G.A. design certified
without modification.
Before checking piping, check with gas company or au-
thorities having jurisdiction for local code requirements.
Refer to the LGA/LGC Installation, Operation and Main-
tenance instruction for more information.
GAS PIPING COMPONENTS
REFER TO INSTALLATION INSTRUCTIONS
GROUND
JOINT UNION
MANUAL MAIN
SHUT−OFF VALVE
(REFER TO LOCAL CODES)
FIGURE 33
1−Gas Piping
Gas supply piping must not allow more than 0.5"W.C.
(124.3 Pa) drop in pressure between the gas meter and
the unit. Supply gas pipe must not be smaller than the unit
gas connection. Refer to installation instructions for de-
tails.
2−Testing Gas Piping
NOTE−In case emergency shutdown is required, turn off
the main manual shut-off valve and disconnect the main
power to the unit. These controls should be properly la-
beled by the installer.
When pressure testing gas lines, the gas valve must be dis-
connected and isolated. Gas valves can be damaged if sub-
jected to more than 0.5 psig [14"W.C. (3481 Pa)]. See figure
33.
When checking piping connection for gas leaks, use the
preferred means. Common kitchen detergents can
cause harmful corrosion on various metals used in gas
piping. The use of 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.
VALVE
CAP HERE TO ISO-
UNIT
LATE VALVE
WHEN PRESSURE
TESTING LINE
ROOF
MOUNTING
FRAME
DRIP LEG
GAS PIPING
SUPPORT
3−Testing Gas Supply Pressure
When testing gas supply pressure, connect test gauge to the
inlet pressure tap on the gas valve (figure 31 and 32). Test
supply gas pressure with unit firing at maximum rate (both
stages energized). Make sure the reading falls within the
range of the following values. Low pressure may result in
erratic operation or underfire." High pressure can result in
permanent damage to the gas valve or overfire." For nat-
ural gas units, operating pressure at the unit gas connec-
tion must be between 4.7"W.C. and 10.5"W.C. (1168 Pa
and 2610 Pa). For L.P. gas units, operating pressure at
the unit gas connection must be between 10.8"W.C. and
13.0"W.C. (2685 Pa and 3232 Pa).
On multiple unit installations, each unit should be checked
separately while operating at maximum rate, beginning with
the one closest to the supply gas main and progressing to
the one furthest from the main. Multiple units should
also be tested with and without the other units operating.
Supply pressure must fall within the range listed in the
previous paragraph.
4−Check and Adjust Manifold Pressure
After line pressure has been checked and adjusted,
check manifold pressure. Move test gauge to the outlet
pressure tap located on unit gas valve GV1. See table 4 in
GAS HEAT COMPONENT section for proper manifold
pressure and figure 25 for location of pressure tap on the
gas valve.
The manifold pressure is factory set and should not re-
quire adjustment. If manifold pressure is incorrect and no other
source of improper manifold pressure can be found, the valve
must be replaced. Refer to figure 25 for location of gas valve
(manifold pressure) adjustment screw.
All gas valves are factory regulated. The gas valve should
completely and immediately cycle off in the event of gas or
power failure. The manual shut-off knob can be used to imme-
diately shut off gas supply.
For safety, connect a shut-off valve between the
manometer and the gas tap to permit shut off of
gas pressure to the manometer.
Manifold Adjustment Procedure
1− Connect test gauge to the outlet pressure tap on the
gas valve. Start the unit (call for second stage heat)
and allow five minutes for the unit to reach steady
state.
2− While waiting for the unit to stabilize, notice the
flame. The flame should be stable without flashback
and should not lift from the burner heads. Natural
gas should burn basically blue with some clear
streaks. L.P. gas should burn mostly blue with some
clear yellow streaks.
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CAUTION