Daikin DBG Series, Service Instructions Manual

Page: 41 / 108

SERVICING
41
3. Select the proper speed tap or dip switch setting for direct
drive units.
4. For gas heat units, the airflow must be adjusted so that
the air temperature rise falls within the ranges given
stated on Data Plate by adjusting the variable pitch
sheave on the motor (see Blower Performance section
in appropriate Specifications Sheet Manual for correct
pulley adjustment).
5. Take motor amperage draw to determine that the motor
is not overloaded during adjustments.
S-205 CHECKING BELT TENSION
NOTE: Section on high static tables may require a field
motor change.
BELT DRIVE
Tension and Alignment Adjustment
Check drive for adequate run-in belt tension. Correct belt
tension is very important. A belt that is loose will have a sub-
stantially shorter life, and a belt that is too tight may cause
premature motor and bearing failure. Correct belt tension on
these units can be checked by measuring the force required
to deflect the belt 1/8" at the midpoint of the span length
(Figure 21). Belt tension force can be measured using a belt
tension checker, available through most belt manufacturers.
The correct deflection force is 5 Ibs. for a new belt and 3.5
Ibs. for a belt that has been run in. New belt tension includes
initial belt stretch. When new V-belts are installed on a
drive the initial tension will drop rapidly during the first few
hours. Check tension frequently during the first 24 hours of
operation. Subsequent retensioning should fall between the
minimum and maximum force. To determine the deflection
distance from the normal position, use a straightedge or
stretch a cord from sheave to sheave to use as a reference
line. On multiple belt drives, an adjacent undeflected belt
can be used as a reference.
SPAN LENGTH t
*DEFLECTION
FORCE
h
C
d H
D
*Apply force to the center of the span.
t = Span length, inches
C = Center distance, inches
D = Larger sheave diameter, inches
d = Smaller sheave diameter, inches
h = Deflection height, inches
DRIVE BELT TENSION ADJUSTMENT
15&20 TON MODELS
MODEL
SHEAVE
DIAMETER
(in)
DEFLECTION
(in)
BELT DRIVE Used New
15 Ton B, BA Standard 4.3 to 5.5 5.5 + .5 8.2 + .5 1/4 ± 1/16
20 Ton
25 Ton
B, BA Standard 4.3 to 5.5 5.5 + .5 8.2 + .5 1/4 ± 1/16
DEFLECTION
FORCE (lbs)
TYPE
RECOMMENDED POUNDS OF FORCE PER BELT
S-206 INDOOR FAN ROTATION CHECK
Evaporator Fan Rotation Check (Three Phase Models
Only)
Check that fan rotates clockwise when viewed from the drive
side of unit and in accordance with rotation arrow shown
on blower housing. If it does not, reverse any two incoming
power cables at Single Point Power Block. In this case, repeat
bearing check.
Do not attempt to change load side wiring. Internal wiring as-
sures all motors and compressors will rotate in correct direction
once evaporator fan motor rotation check has been made.