Reznor SHH (Indoor PreevA) Unit Installation Manual - Manual (Page 42)

Form I-PDH/SDH/PEH/SHH/PXH, Page 42
6.8.4 Optional
Variable Frequency
Drive (VFD)
6.8 Blowers, Belts,
and Drives
6.8.1 Belts and Belt Tension
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 exces-
sive 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
36.) After correct tension is achieved, re-tighten the locknut on the adjustment screw.
Be sure that the belt is aligned in pulleys.
3/4” (19mm)
FIGURE 36 - Check
Belt Tension
Linked Belts - If the belt needs tightening, the recommended method of tightening the
belt length is to count the number of links and remove one link for every 24. (A link is
made up of two joining sections of belt. For easier removal of links, turn the belt inside
out. But be sure to turn it back before installing. If belt is removed or replaced, be sure
to align directional arrows on the belt to the proper drive rotation.) After the first 24
hours of running at full load and at regular maintenance inspections, check the tension
of the belt. Be sure that the belt is aligned in the pulleys.
Solid Belts - Adjust the belt tension by turning the adjusting screw on the motor base
until the belt can be depressed 3/4” (19mm). (See FIGURE 36.) After correct tension
is achieved, re-tighten the locknut on the adjustment screw. Be sure that the belt is
aligned in the pulleys.
6.0 Mechanical
(cont’d)
If ordered with a VFD, it may be either factory or field installed. If field-installed, follow
the manufacturer’s instructions and refer to the wiring diagram on the unit. Minimum
ambient temperature for a VFD is 18°F. Maximum distance from the unit is 50 feet.
When an optional VFD 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.
6.8.2 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 resis-
tance 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 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 (SDH/PDH/SHH) and the electric power (all models).
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 36.)
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 power (PDH/SDH/PEH/SHH) and the gas (PDH/SDH/SHH). Set the
control to call for heat.
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.
6.8.3 Blower 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.