Checking External Static Pressure; Checking Temperature Rise; Checking Belt Tension - Daikin DCG Series Service Instructions Manual

SERVICING
S-200 CHECKING EXTERNAL STATIC PRES-
SURE
The minimum and maximum allowable duct static pressure
is found in the Specifications Sheet Manual.
Too great of an external static pressure will result in insuffi-
cient air that can cause icing of the coil, whereas too much
air can cause poor humidity control, and condensate to be
pulled off the evaporator coil causing condensate leakage.
Too much air can cause motor overloading and in many
cases this constitutes a poorly designed system. To deter-
mine proper air movement, proceed as follows:
1. Using a draft gauge (inclined manometer) measure the
static pressure of the return duct at the inlet of the unit,
(Negative Pressure).
TOTAL EXTERNAL STATIC
2. Measure the static pressure of the supply duct, (Positive
Pressure).
3. Add the two readings together.
NOTE: Both readings may be taken simultaneously and read
directly on the manometer if so desired.
4. Consult proper table for quantity of air.
If the external static pressure exceeds the minimum or
maximum allowable statics, check for closed dampers, dirty
filters, undersized or poorly laid out ductwork.
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.
62
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.
SUPPLY
RETURN
T
T

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 A A
ENSION AND LIGNMENT
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
T T
RISE = SUPPLY -
DJUSTMENT