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Condensate Drain —
line at unit drain connection. Use 1-in. standard pipe.
Measure maximum design negative static pressure up-
stream from the fan. Referring to Fig. 20, height "H" must be
equal to or larger than negative static pressure at design operat-
ing conditions. Prime enough water in trap to prevent losing
seal (Differential 1). When the fan starts, Differential 2 is equal
to the maximum negative static pressure.
Provide freeze-up protection and insulation as required.
DRAIN NIPPLE
FAN OFF
TRAP CONDITION WHEN FAN STARTS
COOLING COIL
DRAIN PAN
FAN RUNNING AND CONDENSATE DRAINING
Fig. 20 — Condensate Drain
Variable Frequency Drive (VFD) —
quency drives (VFDs) are used to modulate fan motor speed in
response to air volume requirements. To vary the motor speed,
a VFD changes the input frequency and line voltage into a
wide range of frequency and voltage outputs, while maintain-
ing a constant ratio of frequency to voltage.
Since 2001, all 1-hp and greater motors supplied by Carrier
for the 39L series air handling units are designed and construct-
ed for use with variable frequency drives. If a field-supplied
motor is installed, ensure the motor is suitable for use with a
VFD.
If the lead length from the VFD to the motor is greater than
25 ft, Shaft Grounding Rings (SGR) are necessary to help dis-
sipate induced shaft voltages to ground and prevent motor
bearing damage.
Install Fan Motor —
sure electrical junction box is toward the center of the unit.
This is necessary for drive and belts to be properly tightened.
Use smallest slots in motor mounting base that will accommo-
date motor and allow minimum overhang (Fig. 21). Be sure
that motor holddown bolts are tight on field-installed motor.
JUNCTION BOX CONDENSATE PREVENTION —
When air handlers are installed outdoors in a high humidity
environment or indoors where the apparatus room is used as a
fresh air plenum, precautions must be taken to prevent conden-
sation from forming inside the junction box of the internally
mounted motor.
Standard installation practice is to mount the motor starter
or fused disconnect box adjacent to the air handler and enclose
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
[National 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
located inside the unit, the motor temperature is that of the cool
816
Install a trapped condensate drain
DIFFERENTIAL
1
H
DIFFERENTIAL
2
Variable fre-
For field installation of motors, be
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 conduit
to the motor, seal the power wires inside the flexible conduit at
the motor starter or fused disconnect.
Use a nonconductive, nonhardening sealant. Permagum
(manufactured by Schnee Morehead) or sealing compound,
thumb grade (manufactured by Calgon), are acceptable
materials.
POWER KNOCKOUTS — Panels are not provided with
knockouts for the fan motor power wiring. Openings must be
drilled or punched in the exterior panels of the unit. It is recom-
mended that power wiring be routed through the discharge
panel whenever possible, as this panel is rarely removed for
service access.
Install Sheaves on Motor and Fan Shafts —
Factory-supplied drives are prealigned and tensioned, however,
Carrier recommends that you check the belt tension and align-
ment before starting the unit. Always check the drive align-
ment after adjusting belt tension.
When field installing or replacing sheaves, install sheaves
on fan shaft and motor shaft for minimum overhang. (See
Fig. 21.) Use care when mounting sheave on fan shaft; too
much force may damage bearing. Remove rust-preventative
coating or oil from shaft. Make sure shaft is clean and free of
burrs. Add grease or lubricant to bore of sheave before
installing.
The 39L fan, shaft, and drive pulley are balanced as a com-
plete assembly to a high degree of accuracy. If excessive unit
vibration is present after fan pulley replacement, the unit must
be rebalanced. For drive ratio changes, always reselect the mo-
tor pulley — do not change the fan pulley.
ALIGNMENT — Make sure that fan shafts and motor shafts
are parallel and level. The most common causes of mis-
alignment 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
replaced before it has given maximum service. If misalignment
is in the sheave, belts will enter and leave the grooves at an
angle, causing excessive belt cover and sheave wear.
1. Shaft alignment can be checked by measuring the
distance between the shafts at 3 or more locations. If the
distances are equal, then the shafts will be 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 lined up the string
will touch them at the points indicated by the arrows in
Fig. 22.
Adjustable sheave — To check the location of adjustable
sheave on shaft, make sure that the centerlines of both
sheaves are in line and parallel with the bearing support
channel. See Fig. 22. Adjustable pitch drives are installed
on the motor shaft.
With adjustable sheave, do not exceed maximum fan rpm.
3. Rotating each sheave a half revolution will determine
whether the sheave is wobbly or the drive shaft is bent.
Correct any misalignment.
16
CAUTION
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