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Blower Operation and Adjustments
NOTE − These units must not be used as a 4construction
heater" at any time during any phase of construction.
Very low return air temperatures, harmful vapors, and
misplacement of the filters will damage the unit and its
efficiency. Additionally, a unit which will be subject to cold
temperatures when not in operation must have a vapor
barrier installed to seal the duct connections. Failure to
protect the unit from moisture laden air or harmful vapors
(generated
from
the
construction
process
and
temporary combustion heating equipment) will cause
corrosive condensation within the unit. Failure to
properly protect the unit in this situation will cause
electrical and electronic component failure and could
affect the unit warranty status.
A−Blower Operation
1− Blower operation is manually set at the thermostat
subbase fan switch. With fan switch in ON position,
blowers will operate continuously.
2− With fan switch in AUTO position, the blower will cycle
with demand. Blower and entire unit will be off when
system switch is in OFF position.
B−Determining Unit CFM
1− The following measurements must be made with a
dry indoor coil. Run blower without a cooling demand.
Air filters must be in place when measurements are
taken.
2− Measure static pressure external to unit (from supply
to return).
3− Measure the indoor blower wheel RPM.
4− Refer to unit nameplate to determine the blower
motor horse power.
5− Referring to table 2 or 3, use the static pressure and
RPM readings to determine unit CFM.
6− The CFM can be adjusted at the motor pulley (see
section C−Blower Belt Adjustment).
C−Blower Belt Adjustment
Maximum life and wear can be obtained from belts only if
proper pulley alignment and belt tension are maintained.
Important−Tension new belt after a 24−48 hour period of
operation. This will allow belts to stretch and seat
grooves. To increase belt tension, loosen 2 locking bolts
and pull mounting plate. Tighten motor mounting plate in
vertical position. See figure 13.
FIGURE 13
BLOWER SPEED ADJUSTMENT
BLOWER
WHEEL
MOTOR & PULLEY
TO INCREASE CFM
LOOSEN ALLEN SCREW &
TURN PULLEY CLOCKWISE
TO DECREASE CFM
TURN PULLEY
COUNTERCLOCKWISE
TO INCREASE BELT TENSION
1 − Loosen 2 locking bolts.
2 − Pull motor mounting plate.
3 − Tighten motor mounting plate so plate is vertical.
MOTOR MOUNTING PLATE
LOCKING BOLTS
BELT
SET
SCREW
KEY
D−Check Belt Tension
Overtensioning belts shortens belt and bearing life.
Check belt tension as follows:
1− Measure span length X. See figure 14.
2− Apply perpendicular force to center of span (X) with
enough pressure to deflect belt 1/64" for every inch of
span length or 1.5mm per 100mm of span length.
Example: Deflection distance of a 40" span would be
40/64" or 5/8".
Example: Deflection distance of a 400mm span
would be 6mm.
3− Measure belt deflection force. For a used belt, the
deflection force should be 5 lbs. (35kPa) . A new belt
deflection force should be 7 lbs. (48kPa).
A
force
below
these
values
indicates
an
undertensioned belt. A force above these values
indicates an overtensioned belt.
MEASURE BELT TENSION
FIGURE 14
DEFLECTION 1/64" PER INCH OF SPAN
OR 1.5mm PER 100mm OF SPAN
FORCE
