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FIGURE 19
TRANSDUCER
(PART #78H5401)
Page 20
TABLE 17
Unit
CO
2
%
For Nat
CO
2
%
For L.P.
24A−45
5.8 − 6.8
6.8 − 7.8
36A−45
5.4 − 6.4
6.10 − 7.10
36A−070
6.6 − 7.6
7.3 − 8.3
36B−090
6.9 − 7.9
8.2 − 9.2
48B−070
6.0 − 7.0
5.7 − 6.7
48C−090
7.2 − 8.2
7.7 − 8.7
48C−110
6.8 − 7.8
7.8 − 8.8
60C−110
6.8 − 7.8
7.8 − 8.8
60D−135
6.9 − 7.9
7.8 − 8.8
H−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 opera-
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 sig-
nal. Seefigure19. The
transducer converts mi-
croamps to volts on a 1:1 conversion. See table 18 for flame
signal A digital readout meter must be used. The transduc-
er plugs into most meters. See figure 20 for proper use of
transducer.
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.
TABLE 18
Flame Signal in Microamps
SureLight
Control
Normal
Low
Drop Out
56L84
10M90
32M88
0.18
0.16 − 0.17
0.15
69M08
0.31
0.25 − 0.30
0.24
78M47
100973−01
1.5
0.5 − 1.4
0.4
SET DIAL TO
MEASURE VDC
(+)
(−)
(−) TO
FLAME
SENSOR
NOTE−MUST USE DIGITAL METER
RED COLLAR
INDICATES
POSITIVE
LEAD
(+) TO
IGNITION
CONTROL
SENSOR
WIRE
FIGURE 20
WARNING
Fire and explosion hazard.
These instructions MUST be followed exactly.
Can cause a fire or explosion resulting in property
damage, personal injury or loss of life.
V−TYPICAL OPERATING CHARACTERISTICS
A−Blower Operation and Adjustment
NOTE− The following is a generalized procedure and
does not apply to all thermostat controls.
1 − Blower operation is dependent on thermostat control
system.
2 − Generally, blower operation is set at thermostat sub-
base fan switch. With fan switch in ON position, blower
operates continuously. With fan switch in AUTO position,
blower cycles with demand or runs continuously while
heating or cooling circuit cycles.
3 − Depending on the type of indoor thermostat, blower
and entire unit will be off when the system switch is in
OFF position.