Carrier 48HC D17 Series Service And Maintenance Instructions page 8

16. Secure the pulley to the motor by tightening the
pulley setscrew to the motor shaft.
17. Insert four bolts and flat washers through mounting
holes on the motor into holes on the motor mounting
plate.
18. On one bolt, place a new external- - tooth lock washer
between the motor and motor mounting band.
19. Ensure the teeth of the external- - tooth lock washer
make contact with the painted base of the motor.
This washer is essential for properly grounding motor.
20. Install four new lock washers and four nuts on the
bolts on the bottom of the motor mounting plate.
21. Do Not tighten the mounting bolts at this time.
22. Set new motor and motor mounting bracket back onto
the unit. See Fig. 10.
23. Install four bolts, four flat washers, four new lock
washers and four nuts attaching the motor assembly
to the unit.
24. Do Not tighten the mounting bolts at this time.
25. Install motor drive V- - belt to motor pulley and blower
wheel pulley. See CAUTION.
26. Align the motor pulley and blower wheel pulley using
a straight edge. See Fig. 6.
27. Adjust the V- - belt tension using adjustment tool.
28. Turn two jack bolts clockwise, moving the motor
assembly away from the blower pulley, increasing the
V- - belt tension.
29. Tighten the four bolts securing the motor mounting
brackets to the unit. Torque four bolts to 120  12
in- - lbs (14  1.4 Nm).
30. Remove cover on motor connection box.
31. Re- - connect all electrical leads to the motor and
replace the connection box cover.
32. Re- - connect all electrical power to the unit. Remove
lockout tags on all electrical power sources.
33. Start unit and allow to run for a designated period.
34. Shut off unit and make any necessary adjustments to
the V- - belt tension or the motor and blower wheel
pulley alignment.
1/2"
(1.3 cm)
BELT
DEFLECTION
Fig. 11 - - Adjusting V- - belt Tension
STRAIGHTEDGE
BROWNING BELT
TENSION CHECKER
C12093
Changing Fan Wheel Speed by Changing Pulleys
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 provided on the original factory pulley.
Change fan wheel speed by changing the fixed fan pulley
(larger pitch diameter to reduce wheel speed, smaller
pitch diameter to increase wheel speed) or select a new
system with both pulleys and matching belt(s).
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.
CAUTION
EQUIPMENT DAMAGE HAZARD
Failure to follow this caution can result in equipment
damage.
Drive packages cannot be changed in the field. For
example: a standard drive cannot be changed to a high
static drive. This type of change will alter the unit's
certification and could require heavier wiring to
support the higher amperage draw of the drive
package.
NOTE: Drive packages cannot be changed in the field.
For example: a standard drive cannot be changed to a high
static drive. This type of change will alter the unit's
certification and could require heavier wiring to support
the higher amperage draw of the drive package.
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.
To determine variable pitch pulley diameter perform the
following calculation:
1. Determine full open and full closed pulley diameter.
2. Subtract the full open diameter from the full closed
diameter.
3. Divide that number by the number of pulley turns
open from full closed
This number is the change in pitch datum per turn
open.
EXAMPLE
- - Pulley dimensions 2.9 to 3.9 (full close to full open)
- - 3.9 - - 2.9 = 1
- - 1 divided by 5 (turns from full close to full open)
- - 0.2 change in pulley diameter per turn open
- - 2.9 + 0.2 = 3.1" pulley diameter when pulley closed
one turn from full open
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