Carrier 48TC series, Service And Maintenance Instructions, Page: 7 / 112

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14. Remove the variable pitch pulley from the old motor and
attach it to the new motor.
15. Inspect the variable pitch pulley for cracks and wear. Replace
the pulley if necessary.
16. Secure the pulley to the motor by tightening the pulley set -
screw to the motor shaft.
17. Insert four bolts and flat washers through the mounting holes
on the motor and 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. Make sure the teeth of the external-tooth lock washer make
contact with the painted base of the motor. This washer is
essential for properly grounding the motor.
20. Install four new lock washers and four nuts on the bolts on the
bottom of the motor mounting plate, but do not tighten the
mounting bolts at this time.
21. Set the new motor and motor mounting bracket back onto the
unit.
22. Install four bolts, four flat washers, four new lock washers
and four nuts attaching the motor assembly to the unit, but do
not tighten the mounting bolts at this time.
23. Install the motor drive V-belt to the motor pulley and blower -
wheel pulley. See CAUTION on page 6.
24. Align the motor pulley and blower wheel pulley using a
straight edge. See Fig. 7.
25. Adjust the V-belt tension using the adjustment tool.
26. Turn the two jack bolts clockwise, moving the motor
assembly away from the blower pulley, increasing the V-
belt tension.
27. Tighten the four bolts securing the motor mounting brackets
to the unit. Torque bolts to 120 ± 12 in.-lb (14 ± 1.4 Nm).
28. Remove the cover on the motor connection box.
29. Re-connect all electrical leads to the motor and replace the
connection box cover.
30. Re-connect all electrical power to the unit. Remove lockout
tags on all electrical power sources.
31. Start the unit and allow to run for a designated period.
32. Shut off the unit and make any necessary adjustments to
the V-belt tension or the motor and blower wheel pulley
alignment.
Fig. 11 — Adjusting V-belt Tension
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 con -
dition. 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 adjust -
ment). This will reduce the amount of vibration generated by the
motor/belt-drive system.
To determine variable pitch pulley diameter, perform the follow -
ing 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-in.
• 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-in. pulley diameter when pulley closed one
turn from full open
CONDENSER COIL SERVICE
Round Tube Plate Fin (RTPF) Condenser Coil
The condenser coil is fabricated with round tube copper hairpins
and plate fins of various materials and/or coatings (see the Model
Number Nomenclature in Appendix A to identify the materials
provided in this unit). The coil may be one-row or composite-type
two-row. Composite two-row coils are two single-row coils fabri -
cated with a single return bend end tubesheet.
RECOMMENDED CONDENSER COIL MAINTENANCE
AND CLEANING
Routine cleaning of coil surfaces is essential to maintain proper
operation of the unit. Elimination of contamination and removal of
harmful residues will greatly increase the life of the coil and ex -
tend the life of the unit. The following maintenance and cleaning
procedures are recommended as part of the routine maintenance
activities to extend the life of the coil.
Remove Surface Loaded Fibers
Surface loaded fibers or dirt should be removed with a vacuum
cleaner. If a vacuum cleaner is not available, a soft non-metal -
lic bristle brush may be used. In either case, the tool should be
applied in the direction of the fins. Coil surfaces can be easily
BROWNING BELT
TENSION CHECKER
STRAIGHTEDGE
1/2”
(1.3 cm)
BELT
DEFLECTION
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 re -
quire heavier wiring to support the higher amperage draw of
the drive package.