Fan Motors And Drives; Motor Power Wiring; Sheaves - Carrier AERO 39MN Installation, Start-Up And Service Instructions Manual

Fan Motors and Drives —
the field, locate the electrical junction box toward the center
of the unit. This arrangement is required for correct belt ten-
sion. Use the smallest mounting holes in the mounting base
that will accommodate the motor and provide minimum over-
hang.
Tighten the motor holddown bolts. Refer to Table 2B for
fan scroll inlet cone dimensions.
JUNCTION BOX CONDENSATE PREVENTION — When
air handlers are installed outdoors in a high humidity envi-
ronment or indoors where the apparatus room is used as a
fresh air plenum, precautions must be taken to prevent con-
densation from forming inside the junction box of the inter-
nally mounted motor.
Standard installation practice is to mount the motor starter
or fused disconnect box adjacent to the air handler and en-
close the power wiring to the motor in flexible conduit.
The sheet metal housing of the disconnect switch or motor
starter is not airtight (even when a box meeting NEMA [Na-
tional Electrical Manufacturers Association] IV standards is
used). Thus, warm moist air can migrate through the flexible
conduit to the junction box on the motor. With the motor lo-
cated inside the unit, the motor temperature is that of the cool
supply air; thus, condensate can form inside the junction box
and, possibly, on the live terminal lugs.
To prevent the moist air from migrating through the con-
duit to the motor, seal the power wires inside the flexible con-
duit at the motor starter or fused disconnect (Fig. 34).
Use a nonconductive, non-hardening sealant. Permagum
(manufactured by Schnee Morehead) or sealing compound,
thumb grade (manufactured by Calgon), are acceptable
materials.
Fig. 34 — Sealing Power Wires in Flexible Conduit
Motor Power Wiring —
with a decal indicating the recommended location to drill or
punch hole(s) to accommodate an electrical conduit for the
fan-motor wiring. The decal is located on the motor side,
approximately 4-in. in from the side and 4-in. down from the
top of the corner above where the motor will be installed.
Where possible, the conduit should be installed in a panel
which will not be removed, such as the discharge panel.
MOTOR OVERLOAD PROTECTION — Fan-motor start-
ers and overload protectors are field-supplied and installed. A
label on the fan motor indicates the correct size of the over-
load protectors required to be installed in the motor starter.
Factory-supplied drives are pre-aligned and
Sheaves —
tensioned, however, Carrier recommends checking the belt
tension and alignment before starting the unit. Always check
the drive alignment after adjusting belt tension.
To install sheaves on the fan or motor shaft, remove any
rust-preventive coating on the shaft. Make sure the shaft is
clean and free of burrs. Add grease or lubricant to bore of
sheave before installing. Mount sheave on the shaft; to pre-
vent bearing damage, do not use excessive force (i.e., a ham-
mer). Place sheaves for minimum overhang (see Fig. 35).
Each factory-assembled fan, shaft, and drive sheave as-
sembly is precision aligned and balanced. If excessive unit vi-
bration occurs after field replacement of sheaves, the unit
When installing motors in
a39-1108tf
The fan section is provided
should be rebalanced. To change the drive ratio, reselect and
replace the motor sheave, not the fan sheave.
After 24 hours of unit operation, the drive belts may
stretch. Check the belt tension after 24 hours of operation and
adjust if necessary. Periodically check belt tension throughout
the run-in period, which is normally the initial 72 hours of
operation.
Fig. 35 — Determining Sheave-Shaft Overhang
ALIGNMENT — Make sure that fan shafts and motor shafts
are parallel and level. The most common causes of misalign-
ment are nonparallel shafts and improperly located sheaves.
Where shafts are not parallel, belts on one side are drawn
tighter and pull more than their share of the load. As a result,
these belts wear out faster, requiring the entire set to be re-
placed before it has given maximum service. If misalignment
is in the sheave, belts enter and leave the grooves at an angle,
causing excessive belt and sheave wear.
1. Shaft alignment can be checked by measuring the dis-
tance between the shafts at 3 or more locations. If the
distances are equal, then the shafts are parallel.
2. Sheave Alignment:
Fixed sheaves — To check the location of the fixed
sheaves on the shafts, a straightedge or a piece of string
can be used. If the sheaves are properly aligned, the
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