Reznor RPB Unit Installation Manual - Manual (Page 23)

Form I-RPB, P/N 131782 R12, Page 23
6.5.3 Blower Rotation Each blower housing is marked for proper rotation. Rotation may be changed on sin-
gle-phase motors by re-wiring in the motor terminal box. Three-phase motors may be
reversed by interchanging two wires on the 3-phase supply connections.
6.5.4 Airflow Proving
Switch (Makeup
Air only) - Outdoor
Models with Option
BW1
The optional airflow proving switch ensures that the circulating air blower is function-
ally providing an adequate amount of airflow prior to the unit being fired. The switch is
a single pole/normally open device which closes when an increase in pressure, above
the setpoint, is sensed in the circulating air blower. The switch is located in the blower
junction box. (See FIGURE 29, Item 40).
Contacts are set to close at .10" w.c. (+.05" or -.02" w.c.).
6.5.5 Optional
Variable Frequency
Drive
When an optional variable frequency drive is ordered, the motor operates on two
speeds as determined by the electrical frequency. High speed is used for cooling and
low speed for heating. 60 hertz is the maximum high speed. Maximum speed for low
speed heating is the frequency that will provide the maximum temperature rise of the
heater.
Follow the variable frequency controller manufacturer's instructions that are packaged
with the heater (in the owner's envelope) to program the variable frequency drive set-
tings. The formula for motor speed is N=120xf/p where N is speed; f is frequency; and
p is number of poles (3600 RPM motor has 2 poles; an 1800 RPM motor has 4 poles).
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 will increase outlet temperature; increasing
blower speed will decrease 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 which permits
adjustment of the blower speed. Follow these instructions to adjust the blower speed.
1. Turn off the gas and the electric power.
2. Loosen belt tension and remove the belt.
3. Loosen the setscrew on the side of the pulley away from the motor.
4. To increase the blower speed, decreasing outlet temperature, turn the
adjustable half of the pulley inward. To decrease the blower speed, increasing
the outlet temperature, turn the adjustable half of the pulley outward. One turn of
the pulley will change the speed 8-10%.
5. Tighten the setscrew on the flat portion of the pulley shaft.
6. Replace the belt and adjust the belt tension. Adjust tension by turning the adjusting
screw on the motor base until the belt can be depressed 3/4" (19mm). See
FIGURE 25. Re-tighten the lock nut on the adjusting screw. Be sure that the belts
are aligned in the pulley grooves properly and are not angled from pulley to pulley.
7. Turn on the gas and electric. Light the heater following the instructions on the
lighting instruction plate.
8. Check the motor amps with an amp meter. The maximum motor amp rating on the
motor nameplate must not be exceeded.
When service is complete, check for proper operation.
Example: 1800 RPM motor on 60Hz; N = 120 x 60/4 = 1800
1800 is synchronous speed; assume 2% slip.
Motor will run between 1750 and 1790 RPM at full load depending on
design. Run the same motor at 45Hz (120 x 45/4 = 1350). 1350 RPM less
2% slip equals about 1300 RPM.