1. Check the type of gas being supplied. Be sure that it is the
same as listed on the unit nameplate.
2. Make sure that the vent and combustion air hoods have
been properly installed.
BURNER AIR SHUTTER ADJUSTMENT
Adjust burner shutters so no yellow flame is observed in the
heat exchanger tubes. Refer to Figure 14.
CHECKING SUPPLY AIR CFM
The RPM of the supply air blower will depend on the required CFM,
the unit accessories and the static resistances of both the supply
and the return air duct systems. With this information, the RPM for
the supply air blower can be determined from the blower
performance data in Tables 5 and 6.
Knowing the required blower RPM and the blower motor HP,
the setting (turns open) for the supply air motor pulley can be
determined from Table 11.
BELT DRIVE BLOWER
All units have belt drive single-speed blower motors. The
variable pitch pulley on the blower motor can be adjusted to
obtain the desired supply air CFM. Tighten belts enough to
prevent slipping. but do not over tighten. Belt deflection should
be between 1/4" and 1/2" per foot. Refer to Table 8 for blower
motor and drive data.
Start the supply air blower motor. Adjust the resistances in both
the supply and the return air duct systems to balance the air
distribution throughout the conditioned space. The job
specifications may require that this balancing be done by
someone other than the equipment installer.
To check the supply air CFM after the initial balancing has been
completed:
1. Remove the dot plugs from the holes in the filter access and
blower access panels as shown in Figure 10.
2. Insert at least 8" of 1/4 inch tubing into each of these holes
for sufficient penetration into the air flow on both sides of
the evaporator (or indoor) coil.
NOTE: The tubes must be inserted and held in a position
perpendicular to the air flow so that velocity pres-
sure will not affect the static pressure readings.
3. Using an inclined manometer, determine the pressure drop
across a dry indoor coil. Since the moisture on an indoor
coil may vary greatly, measuring the pressure drop across
a wet coil under field conditions would be inaccurate. To
assure a dry coil, the compressors should be deactivated
while the test is being run.
4. Knowing the pressure drop across a dry coil, the actual
CFM through the unit can be determined from the curve in
Figure 16.
WARNING: Failure to properly adjust the total system air quan-
tity can result in extensive blower damage.
FIG. 14 - TYPICAL FLAME APPEARANCE
TURNS
OPEN*
BLOWER DRIVE RANGE (RPM)
DCG090, 102
DCG120, 150
5
975
860
4
1024
906
3
1073
952
2
1122
998
1
1171
1044
0
1220
1090
*Pulleys can be adjusted in half-turn increments.
ADJUSTMENT
TABLE 11 - SUPPLY AIR BLOWER MOTOR PULLEY
FIG. 15 - PRESSURE DROP ACROSS A DRY INDOOR
COIL VS SUPPLY AIR CFM
530.18-N10Y
Unitary Products Group
15
