11
Utilization Voltage -
The voltage of the line terminals
of the equipment at which the equipment must give fully
satisfactory performance. Once it is established that supply
voltage will be maintained within the utilization range under
all system conditions, check and calculate if an unbalanced
condition exists between phases. Calculate percent voltage
unbalance as follows:
Three Phase Models Only
3) PERCENT VOLTAGE
UNBALANCE
2) MAXIMUM VOLTAGE DEVIATIONS
FROM AVERAGE VOLTAGE
1) AVERAGE VOLTAGE
HOW TO USE THE FORMULA:
EXAMPLE: With voltage of 220, 216, and 213
1) Average Voltage = 220+216+213=649 / 3 = 216
2) Maximum Voltage Deviations from Average Voltage = 220 - 216 = 4
3) Percent Voltage Unbalance = 100 x
=
= 1.8%
Percent voltage unbalance MUST NOT exceed 2%
.
4
216
400
216
= 100 X
AIR FLOW ADJUSTMENTS
When the final adjustments are complete, the current draw
of the motor should be checked and compared to the full
load current rating of the motor. The amperage must not
exceed the service factor stamped on the motor nameplate.
If an economizer is installed, check the unit operating
balance with the economizer at full outside air and at
minimum outside air.
High stage airflow setting to be between 300 and 500 CFM
per ton, see Table below. For models with electric heat the
total airflow must not be less than that required for operation
of the electric heaters. See Appendix D for minimum airflow
for specific electric heaters.
NOTE: Never run CFM below 300 CFM per ton,
evaporator freezing or poor unit performance
is possible.
High Stage Airflow Setting, CFM
(without electric heat)
BELT DRIVE MODELS ONLY
The drive on the supply fan is typically set in the middle
of the RPM range. The drive motor sheave pitch diameter
is field adjustable for the required airflow. Refer to “Motor
Sheave Adjustments” section.
Upon completion of the air flow balancing, we recommend
replacing the variable pitched motor sheave with a
properly-sized fixed sheave. A matching fixed sheave
will provide longer belt and bearing life and vibration free
operation. Initially, it is best to have a variable pitched
motor sheave for the purpose of airflow balancing, but once
the balance has been achieved, fixed sheaves maintain
alignment and minimize vibration more effectively.
For direct drive units, move fan speed wire.
Bearing Check
Prior to energizing any fans, check and make sure that all
setscrews are tight so that bearings are properly secured
to shafts.
Tension and Alignment Adjustment
Correct belt tension is very important to the life of your belt.
Too loose a belt will shorten its life; too tight, premature
motor and bearing failure will occur. Check you belt drive
for adequate “run-in” belt tension by measuring the force
required to deflect the belt at the midpoint of the span length.
Belt tension force can be measured using a belt tension
gauge, available through most belt drive manufacturers.
S
PAN L
E
N
GTH
t
*
DE
FL
E
C
TI
ON
FORC
E
h
C
d
H
D
*Apply force to the center of the span.
BELT TENSION ADJUSTMENT
t = Span length, inches
C = Center distance, inches
D = Larger sheave diameter, inches
d = Smaller sheave diameter, inches
h = Deflection height, inches
BELT DRIVE
USED
NEW
AX
Standard
3.0 to 4.0 4.2 ± 0.5 5.5 ± 0.5
0.313
DEFLECTION
FORCE (lbs)
TYPE
DEFLECTION
(in)
SMALL
SHEAVE
DIAMETER
(in)
RECOMMENDED POUNDS OF FORCE PER BELT
New V-belts will drop rapidly during the first few hours of
use. Check tension frequently during the first 24 hours of
operation. Tension should fall between the minimum and
maximum force. To determine the deflection distance from
a normal position, measure the distance from sheave to
sheave using a straightedge or a cord. This is your reference
line. On multiple belt drives, an adjacent undeflected belt
can be used as a reference.
MOTOR SHEAVE ADJUSTMENTS
Vl, Vm, & 2vp Variable Pitch Key Type Motor
Sheaves
The driving and driven motor sheaves should be in
alignment with each other and the shafts parallel.
Vl & Vm Sheaves Adjustment
1. Loosen set screw “B” using a 5/32” Allen key.
2. Making half or full turns from closed position, adjust
sheave pitch diameter for desired speed. DO NOT
OPEN MORE THAN FIVE FULL TURNS.
3. Tighten set screw “B” securely over flat.
4. Carefully put on belts and adjust belt tension. DO
NOT FORCE BELTS OVER GROOVES.
5. Ensure all keys are in place and the set screws tight
