175619-XIM-C-0109
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Johnson Controls Unitary Products
2.
Insert at least 203 mm (8") of 6.4 mm (1/4”) tubing
into each of these holes for sufficient penetration
into the air flow on both sides of the indoor coil.
NOTE:
The tubes must be inserted and held in a posi-
tion perpendicular to the air flow so that veloc-
ity pressure will not affect the static pressure
readings.
3.
Using an inclined manometer, determine the pres-
sure 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 compressors should be deac-
tivated while the test is being run.
4.
Knowing the pressure drop across a dry coil, the
actual air flow rate through the unit can be deter-
mined from the curve in Pressure Drop vs. Supply
Air Flow rate (Figure 13).
After readings have been obtained, remove the tubes
and reinstall the two 8 mm (5/16”) dot plugs that were
removed in Step 1.
NOTE:
De-energize the compressors before taking
any test measurements to assure a dry indoor
coil.
Failure to properly adjust the total system air
quantity can result in extensive blower dam-
age.
FIGURE 13 - PRESSURE DROP ACROSS COIL
