Daikin DCH048 SERIES, Service Instructions Manual

Page: 38 / 139

SERVICING
38
S-201 CHECKING TEMPERATURE RISE
Temperature rise is related to the BTUH output of the unit and
the amount of air (CFM) circulated over the heat exchanger.
All units are designed for a given range of temperature
increase. This is the temperature of the air leaving the unit
minus the temperature of the air entering the unit.
The more air (CFM) being delivered through a given unit the
less the rise will be; so the less air (CFM) being delivered, the
greater the rise. The temperature rise should be adjusted in
accordance to a given unit specifications and its external
static pressure.
1. Check BTUH input to unit do not exceed input rating
stamped on rating plate.
2. Take entering and leaving air temperatures.
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 Spec Sheet Manual for correct pulley
adjustment).
5. Take motor amperage draw to determine that the motor is
not overloaded during adjustments.
RISE = SUPPLY -
T T
T
T
SUPPLY
RETURN
CHECKING TEMPERATURE RISE
S-205 CHECKING BELT TENSION
NOTE: Section on high static tables may require a field motor
change.
BELT DRIVE MODELS ONLY
T
ENSION AND
A
LIGNMENT
A
DJUSTMENT
Check drive for adequate run-in belt tension. Correct belt
tension is very important. A belt that is loose will
have a
substantially 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 (See
DRIVE BELT TENSION ADJUSTMENT Figure). Belt tension
force can be measured using a belt tension gauge, 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.
* 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