Page 58
31-5000723 Rev. 0
Typical Operating Characteristics
Blower Operation and Adjustment
1.
Blower operation is dependent on thermostat control
system.
2.
Generally, blower operation is set at thermostat subbase
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.
Temperature Rise
Temperature rise for NF97UM 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
horizontal 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
second-stage heat. If using a single-stage thermostat
furnace must fire at least 10 minutes before switching to
second-stage heat.
3.
After plenum thermometers have reached their highest
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, increase
blower speed to reduce temperature.
External Static Pressure
1.
Tap locations shown in Figure 50.
+
-
Figure 50. Static Pressure Test
2.
Punch a 1/4” diameter hole in supply and return air
plenums. Insert manometer hose flush with inside
edge of hole or insulation. Seal around the hose with
permagum. Connect the zero end of the manometer to
the discharge (supply) side of the system. On ducted
systems, 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 blower
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. in the heating mode and must not exceed 1.0” W.C
in the cooling mode.
5.
Seal the hole when the check is complete.
