5808011-JIM-A-0320
Johnson Controls Ducted Systems 57
3. Use an inclined manometer or Magnehelic® to determine
the pressure drop across the unit. This is the external static
pressure (ESP). In order to obtain an accurate
measurement, verify that the air filters are clean.
4. Determine the number of turns the variable motor sheave
is open.
5. Select the correct blower performance table for the unit
from Tables 18 and 19. Tables are presented for side and
bottom duct configuration.
6. Determine the unit measured CFM from the blower
performance table, external static pressure, and the
number of turns the variable motor sheave is open.
7. To adjust measured CFM to required CFM, see Supply air
drive adjustment on page 58.
8. After you note the reading, remove the tubes and seal the
holes.
9. Tighten the blower pulley and motor sheave set screws
after any adjustments. Re-check the set screws after 10-12
hours run time.
Note: You must repeat this procedure with the addition of
field-installed accessories.
Figure 28: Dry coil delta P
Failure to properly adjust the total system air quantity
can result in extensive blower damage.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500
Airflow (CFM)
Dry Coil Delta P (iwg)
J08ZB
J10ZB
J12ZB
J06ZB
J07ZB
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