FIGURE 21
TRANSDUCER
(PART #78H5401)
Page 17
Manifold Adjustment Procedure:
1 - Connect a test gauge to outlet pressure tap on gas
valve. Start unit and allow 5 minutes for unit to reach
steady state.
2 - 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.
3 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to values given in
table 9.
NOTE-Shut unit off and remove manometer as soon as
an accurate reading has been obtained. Take care to
replace pressure tap plug.
F- Proper 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 revoluĆ
tions assures a more accurate time.)
Divide by two
and compare to time in table 10 below. Adjust manĆ
ifold pressure on gas valve to match time needed.
NOTE- To obtain accurate reading, shut off all other
gas appliances connected to meter.
TABLE 10
GAS METER CLOCKING CHART
Seconds for One Revolution
80UHG
U it
Natural
LP
Unit
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
-45
80
160
200
400
-60
60
120
150
300
-100
36
72
90
180
-120
30
60
75
150
Natural-1000 btu/cu ft LP-2500 btu/cu ft
IMPORTANT
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
G-Flame Signal
A microamp DC meter is needed to check the flame signal
on the ignition control.
Flame (microamp) signal is an electrical current which passes
from the furnace control through the sensor during unit operaĆ
tion. Current passes from the sensor through the flame to
ground to complete a safety circuit.
To Measure Flame Signal - Ignition Control:
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. ĂSeeĂfigĆ
ureĂ21. The transducer
converts microamps to volts on a 1:1 conversion. Flame sigĆ
nal should for the EGC control should be 1.0 - 5.0 with a lock-
out signal of .45 nominal microamps, therefore a reading of
1.0 - 5.0 nominal volts should be read on the meter. Flame
signal for the SureLight control should read 0.7 microamps
with a lockout signal of .15 microamps. A digital readout meter
must be used. The transducer plugs into most meters.
See figure 22 for proper use of transducer.
1 - Set the volt meter to the DC voltage scale. Insert
transducer into the VDC and common inputs. ObĆ
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 senĆ
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.
SET DIAL TO MEASURE VDC
(+)
(-)
(-) TO
FLAME SENSOR
NOTE-MUST USE DIGITAL METER
RED COLLAR
INDICATES
POSITIVE
LEAD
(+) TO
IGNITION
CONTROL
SENSOR
WIRE
FIGURE 22
