Reznor SCE Unit Installation Manual - Manual (Page 24)

Form RZ-NA I-SCE, Page 24
3/4” (19mm)
FIGURE 22 - Check Belt
Tension
17. Blowers, Belts
and Drives
Check belt tension. Proper belt tension is important to the long life of the belt and motor. A
loose belt will cause wear and slippage. Too much tension will cause excessive motor and
blower bearing wear. Adjust the belt tension by turning the adjusting screw on the motor
base until the belt can be depressed 3/4" (19mm). (See FIGURE 22.) After correct tension is
achieved, re-tighten the locknut on the adjustment screw. Be sure that the belt is aligned in
pulleys.
Adjusting Blower Speed
The blower speed may be adjusted to achieve the desired outlet temperature, as long as the
adjustment is within the temperature rise and the 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 will increase outlet temperature; increasing blower speed will de-
crease outlet temperature.
At final adjustment, amperes should not exceed motor nameplate amp rating. The installa-
tion 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 instruc-
tions 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 set screw 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 set screw 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". (See
FIGURE 22.) 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 ammeter. The maximum motor amp rating on the
motor nameplate must not be exceeded.
When service is complete, check for proper operation.
Blower Rotation
Each blower housing is marked for proper rotation. Rotation may be changed on single-
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.
Optional Variable
Frequency Drive
If the system is equipped with an optional variable frequency drive, the motor will operate on
speeds as determined by the electrical frequency. 60 hertz is maximum speed. Speeds must be
within the temperature rise range of a Model SCE Series 6 heater which is 30-90°F.
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 settings. The
formula for motor speed is N = 120 x f/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).
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.