Proper Gas Flow; Proper Combustion; Flame Signal - Lennox G43UF SERIES Unit Information

Checks of manifold pressure are made as verification of
proper regulator adjustment.
Manifold operating pressure for the G43UF can be measured
at any time the gas valve is open and is supplying gas to the
unit.
TABLE 16
GAS VALVE MANIFOLD PRESSURE W.C.
Natural
L.P.
IMPORTANT
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 Pressure Measurement and Adjustment
1 − Connect test gauge to outlet tap on gas valve.
2 − Disconnect pressure sensing hose from the gas valve.
Plug end of hose using tape or equivalent. Leave hose
barb on gas valve open to atmosphere.
3 − Start unit and allow 5 minutes for unit to reach steady
state.
4 − While waiting for the unit to stabilize, notice the flame.
Flame should be stable and should not lift from burner.
Natural gas should burn blue. L.P. gas should burn
mostly blue with some orange streaks.
5 − After allowing unit to stabilize for 5 minutes, adjust the
manifold pressure on the gas valve if necessary (see
table 16).
6 − When test is complete, reconnect sensing hose to gas
valve barb.
NOTE−Shut unit off and remove manometer as soon as
an accurate reading has been obtained. Take care to re-
place pressure tap plug.
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 17 below. Adjust manifold pressure on gas valve to
match time needed.
NOTE− To obtain accurate reading, shut off all other gas
appliances connected to meter.
TABLE 17
GAS METER CLOCKING CHART
Seconds for One Revolution
G43UF G43UF
Natural
Unit Unit
1 cu ft Dial 2 cu ft Dial
−045 80
−070 51
−090 40
−110 33
−135 27
Natural−1000 btu/cu ft
3.5 + 0.3
10.0 + 0.7
LP
1 cu ft Dial 2 cu ft DIAL
160 200 400
102 129 258
80 100 200
66 82 164
53 67 134
LP−2500 btu/cu ft
G− Proper Combustion
Furnace should operate at least 15 minutes with correct
manifold pressure and gas flow rate before checking com-
bustions. Take sample beyond the flue outlet and
compare to table 18. The maximum carbon monoxide
reading should not exceed 100 ppm.
Unit Btuh
−045
−070
−090
−110
−135
H−Flame Signal
A transducer (Part #78H5401 available from Lennox Repair
Parts) is required to measure flame signal if meter used will not
read a low micro amp signal. See figure 40. The transducer
converts microamps to volts on a 1:1 conversion. Flame signal
for the G43UF−2 and later units should read a minimum 1.5 mi-
croamps with a lockout signal of 0.5 ( G43UF−1 units should
read a minimum 0.18 microamps with a lockout signal of 0.15
microamps). A digital readout meter must be used. The
transducer plugs into most meters.
To Measure Flame Signal:
1 − Set the volt meter to the DC voltage scale. Insert
transducer into the VDC and common inputs. Ob-
serve correct polarities. Failure to do so results in
negative (−) values.
2 − Turn off supply voltage to control.
3 − Disconnect ignition control flame sensor wire from the
flame sensor.
4 − Connect (−) lead of the transducer to flame sensor.
5 − Connect (+) lead of transducer to the ignition control sen-
sor wire.
6 − Turn supply voltage on and close thermostat contacts to
cycle system.
7 − When main burners are in operation for two minutes, take
reading. Remember 1 DC volt = 1 DC microamp.
NOTE−MUST USE DIGITAL METER
(+) TO
IGNITION
CONTROL
SENSOR
WIRE
Page 35
TABLE 18
CO % CO %
2 For Nat 2
6.3 − 7.3 7.4 − 8.4
6.5 − 7.5 7.6 − 8.6
7.0 − 8.0 8.2 − 9.2
SET DIAL TO
MEASURE VDC
TRANSDUCER
PART #78H5401
(+)
(−)
RED COLLAR
INDICATES
(−) TO
POSITIVE
FLAME
LEAD
SENSOR
FIGURE 40
For L.P