33
RPB-IOM (06-22) 131782-B
3/4" (19 mm)
Figure 18. Checking Belt Tension
Adjusting Blower Speed
• Blower speed may be adjusted to achieve the desired outlet temperature as long as the adjustment is within the
temperature rise and static pressure limits shown on the furnace rating plate. Motors are factory-set between
maximum and minimum blower speeds.
• If the duct resistance is low, the blower may deliver too high an air volume. If the resistance is very low, the blower
may deliver excess air to overload the motor, causing the overload protector to cycle the motor. Reducing the
blower speed will correct these conditions. If ductwork is added to an installation, it may be necessary to increase
the blower speed. Decreasing blower speed increases outlet temperature. Increasing blower speed decreases
outlet temperature.
• At final adjustment, amperes should not exceed motor nameplate amp rating. The installation must be adjusted
to obtain a temperature rise within the range specified on the furnace rating plate.
• The belt drive on these units is equipped with an adjustable pulley that permits blower speed adjustment. Adjust
the blower speed as follows:
a. Shut OFF gas and electric power.
b. Loosen belt tension and remove belt.
c. Loosen setscrew on side of pulley away from motor.
d. To increase blower speed and decrease outlet temperature, turn adjustable half of pulley inward. To decrease
blower speed and increase outlet temperature, turn adjustable half of pulley outward. One turn of pulley
changes speed 8–10%.
e. Tighten setscrew on flat portion of pulley shaft.
f. Replace belt and adjust belt tension in accordance with Checking and Adjusting Belt Tension section.
g. Turn ON gas and electric power and light heater in accordance with instructions on lighting instruction plate.
h. Check motor amps using ammeter (maximum motor amp rating on motor nameplate must not be exceeded).
i. When adjustment is complete, check for proper operation.
Reversing Blower Rotation
Each blower housing is marked for proper rotation. Rotation may be changed on single-phase motors by rewiring in
the motor terminal box. Rotation may be changed on three-phase motors by interchanging two wires on the three-
phase supply connections.
Blower Motor Load and Amp Adjustment
• Amps may be adjusted downward by reducing blower rpm or by increasing duct system static pressure. Use an
ammeter to check blower motor amps.
• See the motor rating plate for exact motor specifications. Do not exceed the amp rating on the motor nameplate.
• Table 17, which lists the Full Load Amps (FLA) of blower motors (open) based on Horsepower (HP) and Voltage
(V), can be used for sizing line wiring but should not be interpreted as the exact motor amps.
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