Typical Operating Characteristics; To Measure Temperature Rise - Lennox G71MPP SERIES Unit Information

V−TYPICAL OPERATING CHARACTERISTICS
A−Blower Operation and Adjustment
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.
B−Temperature Rise
Temperature rise for G71MPP 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 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. Unit must operate on sec-
ond−stage heat. If using a single−stage thermostat fur-
nace must fire at least 10 minutes before switching to
second−stage heat.
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.
C−External Static Pressure
1 − Tap locations shown in figure 37.
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. For systems with non−ducted returns,
leave the other end of the manometer open to the at-
mosphere.
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
0.8" W.C.
5 − Seal around the hole when the check is complete.
Page 51
STATIC PRESSURE TEST
FIGURE 37