Lennox F8AUH series Service Manual page 11

50A55 INTEGRATED CONTROL BOARD
(Silicon Carbide Ignition System)
FIGURE 6
4−Flame Sensor
A flame sensor is located on the left side of the burner sup-
port. See figure 8. The sensor is mounted on a bracket in
the burner support and the tip protrudes into the flame en-
velope of the left−most burner. The sensor is fastened to
burner supports and can be removed for service without
removing any part of the burners. During operation, flame
is sensed by current passed through the flame and sens-
ing electrode. The control board allows the gas valve to re-
main open as long as flame signal is sensed.
NOTE − The F8AUH furnace contains electronic com-
ponents that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
TERMINAL DESIGNATIONS
COOL−H
HEAT−H
EAC−H
HUM−H
XFMR−H
LINE−H
LINE−N
HUM−N
EAC−N
XFMR−N
CIR−N
PARK
(FLAME SENSE)
Silicon Carbide Ignitor
9/16 in. 14.7 mm
 1/32 in. 1 mm
NORMAL FLAME SIGNAL 0.2 MICRAMPS
LOW FLAME SIGNAL
MIN. FLAME SIGNAL
1/4 in. 7 mm
 1/32 in. 0.79
BURNER
NORMAL FLAME SIGNAL u 0.7 MICROAMPS
LOW FLAME SIGNAL
MINIMUM FLAME SIGNAL v 0.15 MICROAMPS
SIDE VIEW
Page 11
TABLE 4
Blower − Cooling Speed (120VAC)
Blower − Heating Speed (120VAC)
Electronic Air Cleaner (120VAC)
Humidifier (120VAC)
Transformer (120VAC)
Input (120VAC)
Input (Neutral)
Humidifier (Neutral)
Electronic Air Cleaner (Neutral)
Transformer (Neutral)
Not Used
Alternate Blower Speeds (Dead)
Flame Sensor
1/4 in. 7 mm
 1/32 in. 1 mm
FIGURE 7
 0.2 MICROAMPS
 0.15 MICROAMPS
11/16 in. 18 mm
 1/32 in. 0.79
mm
3/16 in.
4.7 mm
v 0.7 MICROAMPS
FLAME
SENSOR
END VIEW
FIGURE 8
mm