508146-01
Issue 2051
Page 5
5
of 7
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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
GUH97M
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 51.
+
-
Figure 51. 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.
