341849-YIM-A-0108
Johnson Controls Unitary Products
9
CHECKING SUPPLY AIR CFM
To check the supply air CFM after the initial balancing
has been completed:
1.
Remove the two ¼ inch dot plugs in the duct panel.
2.
Insert at least 8 inches of ¼ inch tubing into each of
these holes for sufficient penetration into the air-
flow on both sides of the indoor coil.
3.
Using an inclined manometer, determine the pres-
sure drop across the 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
ensure a dry coil, the compressors should be deac-
tivated 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 Coil Delta P vs. Supply Air CFM
Figure 3.
After readings have been obtained, remove the tubes
and reinstall the two ¼ inch plugs removed in Step 1.
NOTE:
De-energize the compressors before taking any
test measurements to ensure a dry indoor coil.
FIGURE 3 - Coil Delta P vs. Supply Air CFM
Failure to properly adjust the total system air
quantity can result in extensive system damage.
B1HA Coil Delta
B1HA036
Delta Static (IWG)
Airflow (CFM)
B1HA042
Linear B1HA042
Linear B1HA036
Linear B1HA048-60
B1HA048-60
