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A-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.
B-Temperature Rise FIGURE 22
Temperature rise for SL280DFNV units depends on unit
input, blower speed, blower horsepower and static pres-
sure 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.
Return
Supply
Temperatures
TEMPERATURE RISE
Supply Duct Temperature
Return Duct Temperature
_
Temperature Rise =
FIGURE 22
C-External Static Pressure
1 -
Tap locations shown in FIGURE 23.
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. For
heating speed external static pressure drop must
not be more than 0.5” W.C. For cooling speed
external static pressure drop must not be more than
0.8” W.C.
4 -
Seal the hole when the check is complete.
EXTERNAL STATIC PRESSURE
Supply Duct Static
Return Duct
Total Duct Static =
(dry coil)
Return
Supply
High “+”
Low “-”
+
−
or
FIGURE 23
