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V-TYPICAL OPERATING CHARACTERISTICS
A-Blower Operation and Adjustment
When the thermostat is set to “FAN ON,” the indoor blow-
er will run continuously at approximately 38% of the sec-
ond-stage cooling speed when there is no cooling or heat-
ing demand.
When the SL280DFV is running on high fire or low fire
(low fire is 91% of high fire), the indoor blower will run
on the heating speed designated by the positions of DIP
switches 11 and 12. When the SL280DFV is running on
second-stage cool or first-stage cool (second-stage cool
is 70% of firststage cool), the indoor blower will run on the
cooling speed designated by the positions of DIP switches
5 and 6.
B-Temperature Rise
Temperature rise for SL280DFV units depend on unit in-
put, 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 for high fire and low fire.
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 to highest setting. Confirm unit is on
high fire by checking rate.
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.
4 - Repeat on low fire. Do not adjust low fire manifold
pressure.
C-External Static Pressure
1 - Tap locations shown in FIGURE 20.
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. Open all
return air registers and check for clean filter.
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 0.8” W.C. For cooling speed
external static pressure drop must not be more than
1.0” 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 20
VI-MAINTENANCE
WARNING
Disconnect power before servicing unit.
CAUTION
Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and
dangerous operation. Verify proper operation after
servicing.
WARNING
The inner blower access panel and vent pipe must be
securely in place when the blower and burners are
operating. Gas fumes, which could contain carbon
monoxide, can be drawn into living space resulting
in personal injury or death.
WARNING
Electric Shock Hazard. Can cause injury or death.
Unit must be properly grounded in accordance with
national and local codes.
CAUTION
Failure to use properly sized wiring and circuit
breaker may result in property damage. Size wiring
and circuit breaker(s) per Product Specifications
bulletin (EHB) and unit rating plate.
WARNING
Fire Hazard. Use of aluminum wire with this product
may result in a fire, causing property damage,
severe injury or death. Use copper wire only with
this product.
