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9/2019
C-Determining Unit CFM (with wet coil)
Belt Drive Blowers Controlled By An Inverter
IMPORTANT - MSAV
TM
units are factory-set to run the
blower at full speed when there is a blower (G) demand
without a heating or cooling demand. Refer to the
field-provided, design specified CFM for all modes of
operation. Use the following procedure to adjust motor
pulley to deliver the highest CFM called for in the design
spec. See MSAV
TM
Start-Up section to set blower CFM for
all modes once the motor pulley is set.
IMPORTANT - Direct drive variable blower unit CFM is
determined by the Unit Controller. Refer to the Direct Drive
Variable Speed Start-Up section.
1- Measure the indoor blower motor RPM. Air filters must
be in place when measurements are taken.
2- With all access panels in place, measure static
pressure external to unit (from supply to return). Blower
performance data is based on static pressure readings
taken in locations shown in figure 24.
Note - Static pressure readings can vary if not taken where
shown.
3- Referring to tables 7 through 10, use static pressure and
RPM readings to determine unit CFM.
4- The blower RPM can be adjusted at the motor pulley.
Loosen Allen screw and turn adjustable pulley
clockwise to increase CFM. Turn counterclockwise to
decrease CFM. See figure 21, 22, or 23. Do not exceed
minimum and maximum number of pulley turns as
TABLE 2
Minimum and Maximum Pulley Adjustment
Belt
Minimum Turns Open
Maximum Turns Open
A Section
0
5
B Section
1*
6
*No minimum number of turns open when B belt is used on pulleys
6” O.D. or larger.
D-Adjust Belt Tension
Maximum life and wear can be obtained from belts only if
proper pulley alignment and belt tension are maintained.
Tension new belt after a 24-48 hour period of operation.
This will allow belt to stretch and seat to grooves. Make
sure blower and motor pulley are aligned as shown in
figure 25. See figure 21, 22 or 23 to adjust belt tension.
FIGURE 25
PULLEY ALIGNMENT
(TOP VIEW)
BELT
BLOWER
PULLEY
MOTOR
PULLEY
NOT ALIGNED
ALIGNED
E-Check Belt Tension
Overtensioning belts shortens belt and bearing life. Check
belt tension as follows:
1- Measure span length X. See figure 26.
2- Apply perpendicular force to center of span (X) with
enough pressure to deflect belt 1/64” for every inch of
span length or 0.4mm per 25.4mm of span length.
Example: Deflection distance of a 40” span would be
40/64” or 5/8”.
Example: Deflection distance of a 1016mm span would
be 16mm.
3- Measure belt deflection force. The deflection force
should be 7.0 lbs.
A force below these values indicates an
undertensioned belt. A force above these values
indicates an overtensioned belt.
F-Blower Drives
Use the following belt drive tables to determine BHP and
RPM required. Reference table 12 to determine the drive
numbers and table 13 and 14 to determine the
manufacturer's model number.
MEASURE BELT TENSION
FIGURE 26
DEFLECTION 1/64” PER INCH OF SPAN
OR 0.4MM PER 25.4MM OF SPAN
FORCE
