Typical Operating Conditions - Lennox ML193UH045P36B Unit Information

G−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 52. The transducer
converts microamps to volts on a 1:1 conversion. Flame signal
is shown in table 16. A digital readout meter must be used.
The transducer plugs into most meters.
TABLE 16
Normal Flame Signal
Low Flame Signal
Drop Out Signal
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 integrated control flame sensor wire from
the flame sensor.
4 − Connect (−) lead of the transducer to flame sensor.
5 − Connect (+) lead of transducer to the integrated control
sensor 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
INTE-
GRATED (−)
CONTROL
SENSOR
WIRE
FIGURE 52
V−TYPICAL OPERATING CHARACTERISTICS
A−Blower Operation and Adjustment
1 − Blower operation is dependent on thermostat control
system.
 1.50 Microamps
 1.40 Microamps
= 0.50 Microamps
SET DIAL TO
MEASURE VDC
TRANSDUCER
PART #78H5401
(+)
RED COLLAR
INDICATES
(−) TO
POSITIVE
FLAME
LEAD
SENSOR
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.
B−Temperature Rise
Temperature rise 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 op-
eration within the range of 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 hori-
zontal run of the plenum where it will not pick up radiant
heat from the heat exchanger.
2 − Set thermostat for heat call.
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 existing heat tap, turn off power then switch out
speed tap with tap connected to "PARK" . See unit diagram
for blower motor tap colors for each speed.
C−External Static Pressure
1 − Tap locations shown in figure 53.
2 − Punch a 1/4" diameter hole
in supply and return air ple-
nums. Insert manometer
hose flush with inside edge
of hole or insulation. Seal
around the hose with perma-
gum. Connect the zero end
of the manometer to the dis-
charge (supply) side of the system. On ducted sys-
tems, connect the other end of manometer to the return
duct as above.
3 − With only the blower motor running and the evaporator
coil dry, observe the manometer reading. Adjust blow-
er motor speed to deliver the air desired according to
the job requirements.
4 − External static pressure drop must not be more than
0.5" W.C. in the heating mode and must not exceed
0.6" W.C in the cooling mode.
5 − Seal the hole when the check is complete.
Page 38
STATIC PRESSURE TEST
+
−
FIGURE 53