Carrier 50HCQA05 Service And Maintenance Instructions page 8

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. 10.
Fig. 10 - - Supply- - Fan Pulley Adjustment
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. Reset the belt tension
after each realignment.
Inspect 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. Replace pulley if wear is excessive.
Changing the Fan Speed:
1. Shut off unit power supply. Use proper lockout/tagout
procedures.
2. Loosen belt by loosening fan motor mounting nuts.
See Fig. 8.
3. Loosen movable pulley flange setscrew. See Fig. 10.
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 the maximum specified speed.
5. Set movable flange at nearest keyway of pulley hub.
Tighten setscrew and torque to 65- - 70 in- - lb (7.4 to 7.9
Nm).
Aligning Blower and Motor Pulleys:
1. Loosen blower pulley setscrews.
2. Slide blower pulley along blower shaft. Make angular
alignment by loosening motor mounting plate front
and rear bolts.
3. Tighten blower pulley setscrews and motor mounting
bolts. Torque bolts to 65- - 70 in- - lb (7.4 to 7.9 Nm).
4. Recheck belt tension.
Bearings:
The fan system uses bearings featuring concentric split
locking collars. A Torx T- - 25 socket head cap screw is
used to tighten the locking collars. Tighten the locking
collar by holding it tightly against the inner race of the
bearing. Tighten the socket head cap screw. Torque cap
screw to 55- - 60 in- - lb (6.2- - 6.8 Nm). See Fig. 11. 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 can be necessary.
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Fig. 11 - - Tightening Locking Collar
Motor
When replacing the motor, also replace the external- - tooth
lock washer (star washer) under the motor mounting base;
this is part of the motor grounding system. Ensure the
teeth on the lock washer are in contact with the motor's
painted base. Tighten motor mounting bolts and torque to
120  12 in- - lbs (14  1.4 Nm).
Change fan wheel speed by changing the fan pulley
(larger pitch diameter to reduce wheel speed, smaller
pitch diameter to increase wheel speed) or select a new
system (both pulleys and matching belt). The horsepower
rating of the belt is primarily dictated by the pitch
diameter of the smaller pulley in the drive system
(typically the motor pulley in these units). Do not install a
replacement motor pulley with a smaller pitch diameter
than was provided on the original factory pulley.
Before changing pulleys to increase fan wheel speed,
check the fan performance at the target speed and airflow
rate to determine new motor loading (bhp). Use the fan
performance tables or use the Packaged Rooftop Builder
software program. Confirm that the motor in this unit is
capable of operating at the new operating condition. Fan
shaft loading increases dramatically as wheel speed is
increased.
To reduce vibration, replace the motor's adjustable pitch
pulley with a fixed pitch pulley (after the final airflow
balance adjustment). This will reduce the amount of
vibration generated by the motor/belt- - drive system.
8
LOCKING COL-
LAR
T ---25 TORX SOCKET
HEAD CAP SCREW
C11505