Typical Operating Characteristics - Lennox F8AUH series Service Manual

To Measure Flame Signal − Ignition Control:
A transducer is required
to measure flame signal if
meter used will not read a
low micro amp signal.
See figure 17. The trans-
ducer converts micro-
amps to volts on a 1:1
conversion. Flame signal
for the control board should read 0.7 microamps with a lock-
out signal of .15 microamps. A digital readout meter must be
used. The transducer plugs into most meters. See fig-
ure 18 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.
(−)
FLAME SENSOR
(+) TO
IGNITION
CONTROL
SENSOR
WIRE
FIGURE 18
FIGURE 17
NOTE−MUST USE DIGITAL METER
SET DIAL TO MEASURE VDC
RED COLLAR
INDICATES
(+)
POSITIVE
LEAD
(−) TO
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 on heating speed. 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.
B−Temperature Rise
Temperature rise for F8AUH units depends on unit input,
blower speed, blower horsepower and static pressure as
marked on the unit rating plate. The blower speed must be
set for unit operation within the range of AIR TEMP. RISE
°F" listed on the unit rating plate.
To Measure Temperature Rise:
1 − Place plenum thermometers in the supply and return
air plenums. Locate supply air thermometer in the first
horizontal run of the plenum where it will not pick up ra-
diant heat from the heat exchanger.
2 − Set thermostat to highest setting.
3 − After plenum thermometers have reached their high-
est and steadiest readings, subtract the two readings.
The difference should be in the range listed on the unit
rating plate. If the temperature is too low, decrease
blower speed. If temperature is too high, first check
the firing rate. Provided the firing rate is acceptable, in-
crease blower speed to reduce temperature. To
change blower speed taps see the Blower Speed Taps
section in this manual.
Page 16
WARNING