The setting (turns open) for the optional belt-drive supply air
motor pulley can be determined from Table 15.
OPTIONAL BELT-DRIVE BLOWER
All units with belt-drive blowers have single-speed motors. The
variable pitch pulley on the blower motor can be adjusted to
obtain the desired supply air CFM. Refer to Table 7 for blower
motor and drive data. The tension on the belts should be
adjusted as shown in Figure 7.
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 (two)
5
⁄
16
" dot plugs from the holes located on
the filter access panel side of the unit.
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 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 scroll compressors should be
de-energized 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 8.
WARNING: Failure to properly adjust the total system air quan-
tity can result in poor system performance.
5. After readings have been obtained, remove the tubes and
seal the holes with the
5
⁄
16
" dot plugs removed in Step 1.
NOTE: DE-ENERGIZE THE SCROLL COMPRESSORS BE-
FORE TAKING ANY TEST MEASUREMENTS TO
ASSURE A DRY INDOOR COIL.
SECURE OWNER’S APPROVAL
:
When the system is functioning properly, secure the owner’s approval. Show him the
location of all disconnect switches and the thermostat. Teach him how to start and stop the unit and how to adjust temperature
settings within the limitations of the system.
TURNS
OPEN*
BLOWER DRIVE RANGE (RPM)
3 TON
4 TON
5 TON
6 TON
5
4
3
2
1
0
780
842
904
966
1028
1090
790
856
922
988
1054
1120
850
924
998
1072
1246
1220
900
970
1040
1110
1180
1250
*
Pulley can be adjusted in half-turn increments.
TABLE 15 - BELT-DRIVE SUPPLY AIR
MOTOR PULLEY ADJUSTMENT
SPAN LENGTH
DEFL FORCE
* NEVER LOOSEN
(A)
(C)*
(D)
CAUTION
Procedure for adjusting belt tension:
1. Loosen nut (D) from the motor mount.
2. Never loosen nuts (C) from each other while loosening nut (D).
3. Adjust the tension by turning bolt (B).
4. Do not loosen the four nuts (top and bottom) (A); unless additional tensioning
distance is required; immediately re-tighten these bolts if loosened.
5. Use a belt tension checker to apply a perpendicular force to one belt at the
midpoint of the span as shown. The deflection force should be applied
until a specific deflection distance of 4mm (5/32")is obtained. To determine
the deflection distance from normal position, use a straight edge from
sheave to sheave as a reference line. The recommended deflection force
is as follows:
Tension new belts at the max. deflection force recommended for the belt
section. Check the belt tension at least two times during the first 24 hours of
operation. Any re-tensioning should fall between the min. and max.
deflection force values.
6. After adjusting, re-tighten nut (D) against the motor mount taking care not
to loosen nuts (C).
(B)
FIG. 7 - BELT ADJUSTMENT
FIG. 8 - PRESSURE DROP ACROSS A DRY
EVAPORATOR COIL VS SUPPLY AIR CFM,
WITHOUT AIR FILTERS
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
750
1250
1750
2250
2750
3250
3750
036
048
072
NOMINAL CFM
PRE
S
S
URE DROP
(
IWG)
060
530.18-N7Y
Unitary Products Group
15
