4
is on the motor. The pulleys are connected using a “V” type belt.
(See Fig. 4.)
Fig. 4 — Belt Drive Motor Mounting
BELT
Check the belt condition and tension quarterly. Inspect the belt for
signs of cracking, fraying or glazing along the inside surfaces.
Check belt tension by using a spring-force tool (such as Brown
-
ing’s Part Number “Belt Tension Checker” or equivalent tool);
tension should be 6 lb at a
5
/
8
-in. deflection when measured at the
centerline of the belt span. This point is at the center of the belt
when measuring the distance between the motor shaft and the
blower shaft.
NOTE: Without the spring-tension tool, place a straight edge
across the belt surface at the pulleys, then deflect the belt at mid-
span using one finger to a
1
/
2
-in. deflection.
Adjust the belt tension by loosening the four motor mounting nuts
and bolts where the motor bolts to the blower rail. There are two
jack bolts and nuts that are used to slide the motor plate to either
increase or decrease belt tension. There are locking nuts on the
jack bolts that need to be loosened at the motor plate. Turn the jack
bolts clockwise or counter clockwise until the correct belt tension
is achieved. Ensure the fan shaft and motor shaft are parallel prior
to tightening motor plate nuts. (See Fig. 5.)
Fig. 5 — Adjusting Belt Tension
To replace the belt:
1. Use a belt with same section type or similar size. Do not sub
-
stitute a “FHP” type belt. When installing the new belt, do not
use a tool (screwdriver or pry-bar) to force the belt over the
pulley flanges, as this will stress the belt and cause a reduc
-
tion in belt life.
2. Loosen the motor mounting plate front bolts and rear bolts.
3. Push the motor and its mounting plate towards the blower
housing as close as possible to reduce the center distance
between fan shaft and motor shaft.
4. Remove the belt by gently lifting the old belt over one of the
pulleys.
5. Install the new belt by gently sliding the belt over both pul
-
leys and then sliding the motor and plate away from the fan
housing until proper tension is achieved.
6. Check the alignment of the pulleys, adjust if necessary.
7. Tighten all bolts.
8. Check the tension after a few hours of runtime and re-adjust
as required.
ADJUSTABLE-PITCH PULLEY ON MOTOR
The motor pulley is an adjustable-pitch type that allows a servicer
to implement changes in the fan wheel speed to match as-installed
ductwork systems. The pulley consists of a fixed flange side that
faces the motor (secured to the motor shaft) and a movable flange
side that can be rotated around the fixed flange side that increases
or reduces the pitch diameter of this driver pulley. (See Fig. 6.)
As the pitch diameter is changed by adjusting the position of the
movable flange, the centerline on this pulley shifts laterally (along
the motor shaft). This creates a requirement for a realignment of
the pulleys after any adjustment of the movable flange. Also reset
the belt tension after each realignment.
Check the condition of the motor pulley for signs of wear. Glazing
of the belt contact surfaces and erosion on these surfaces are signs
of improper belt tension and/or belt slippage. Pulley replacement
may be necessary.
To change fan speed:
1. Shut off unit power supply and install lock-out tag.
2. Loosen belt by loosening fan motor mounting nuts. (See
Fig. 4.)
3. Loosen movable pulley flange setscrew. (See Fig. 6.)
4. Screw movable flange toward fixed flange to increase speed
and away from fixed flange to decrease speed. Increasing fan
speed increases load on motor. Do not exceed maximum
speed specified.
5. Set movable flange at nearest keyway of pulley hub and
tighten setscrew to torque specifications. Torque pulley set
screw to 72 ± 5 in-lb.
To align fan and motor pulleys:
1. Loosen fan pulley setscrews.
2. Slide fan pulley along fan shaft. Make angular alignment by
loosening motor from mounting.
3. Tighten fan pulley setscrews and motor mounting bolts to
torque specifications.
4. Recheck belt tension.
Step 1: Loosen
motor bolts
Step 2: Loosen jack bolt
lock nuts
Step 3: Loosen or tighten
jack bolts until proper
belt tension is achieved
