292427-BIM-A-0307
16
Unitary Products Group
4.
All pulleys are factory aligned.
5.
All supply air motor pulleys are factory set at 3 “turns
open”.
After the supply air blower motor is operating, adjust the
resistances in both the supply and the return 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.
Drill two 5/16-inch holes in the side panel as shown in
Figure 13.
2.
Insert at least 8" of 1/4 inch tubing into each of these
holes for sufficient penetration into the airflow on both
sides of the evaporator coil.
NOTE:
The tubes must be inserted and held in a position
perpendicular to the airflow so that velocity pressure
will not affect the static pressure readings.
3.
Using an inclined manometer, determine the pressure
drop across a dry evaporator coil. Since the moisture
on an evaporator coil may vary greatly, measuring the
pressure drop across a wet coil under field conditions
would be inaccurate. To assure a dry coil, the refrigera-
tion system should be de-activated 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 15.
If the CFM is above or below the specified value, the supply
air motor pulley may have to be re-adjusted. After one hour of
operation, check the belt and pulleys for tightness and align-
ment.
After readings have been obtained, remove the tubes and
seal up the drilled holes in the side panel 5/16" dot plugs (P/N
029-13880) are available through normal parts ordering pro-
cedures.
NOTE:
Shut down the refrigeration system before taking
any test measurements to assure a dry evaporator
coil.
TABLE 8: SUPPLY AIR BLOWER MOTOR PULLEY
ADJUSTMENT
Turns
Open
Blower (RPM)
060
090
120
180
5
4
3
2
1
0
810
870
930
990
1050
1110
655
700
745
790
835
880
700
750
800
850
900
950
625
660
700
735
775
810
FIGURE 13 - TYPICAL MOTOR MOUNTING
ASSEMBLY
B
A
(DO NOT LOOSEN)
MOTOR
MOTOR MOUNT
C
FIGURE 14 - HOLE LOCATIONS (PRESSURE DROP
READINGS)
Model
Dimensions (in.)
A
B
C
D
060
9-1/2
14-3/4
19
6-3/4
090
3
17
14
8
120
3
17
14
8
180
7
22
18
10
Failure to properly adjust the total system air quan-
tity can result in extensive blower damage.
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