335224-BIM-B-1208
Johnson Controls Unitary Products
45
CHECKING AIR QUANTITY
METHOD ONE
1.
Remove the dot plugs from the duct panel (for location of
the dot plugs see Figures 15 and 16).
2.
Insert eight-inches of 1/4 inch metal tubing into the air-
flow on both sides of the 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.
Use an Inclined Manometer or Magnehelic to determine
the pressure drop across a dry evaporator coil. Since the
moisture on an evaporator coil can vary greatly, measur-
ing the pressure drop across a wet coil under field condi-
tions could be inaccurate. To assure a dry coil, the
compressors should be de-activated while the test is
being run.
NOTE:
De-energize the compressors before taking any test
measurements to assure a dry evaporator coil.
4.
The CFM through the unit can be determined from the
pressure drop indicated by the manometer by referring to
Figure 31. In order to obtain an accurate measurement,
be certain that the air filters are clean.
5.
To adjust Measured CFM to Required CFM, see ’SUP-
PLY AIR DRIVE ADJUSTMENT’.
6.
After readings have been obtained, remove the tubes
and replace the dot plugs
7.
Tighten blower pulley and motor sheave set screws after
any adjustments. Re-check set screws after 10-12 hrs.
run time is recommended.
METHOD TWO
1.
Drill two 5/16 inch holes, one in the return air duct as
close to the inlet of the unit as possible, and another in
the supply air duct as close to the outlet of the unit as
possible.
2.
Using the whole drilled in step 1, insert eight inches of
1/4 inch metal tubing into the airflow of the return and
supply air ducts of the unit.
NOTE:
The tubes must be inserted and held in position per-
pendicular to the airflow so that velocity pressure
will not affect the static pressure readings.
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, be certain 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 19 - 30. Tables are presented for horizontal
and downflow configuration.
6.
Determine the unit Measured CFM from the Blower Per-
formance Table, External Static Pressure and the num-
ber of turns the variable motor sheave is open.
7.
To adjust Measured CFM to Required CFM, see ’SUP-
PLY AIR DRIVE ADJUSTMENT’.
8.
After reading has been obtained, remove the tubes and
seal holes.
9.
Tighten blower pulley and motor sheave set screws after
any adjustments. Re-check set screws after 10-12 hrs.
run time is recommended.
NOTE:
With the addition of field installed accessories
repeat this procedure.
Failure to properly adjust the total system air quan-
tity can result in extensive blower damage.
Failure to properly adjust the total system air quan-
tity can result in extensive blower damage.
