Checking air quantity
1. Remove the dot plugs from the supply and
return air access panels on the back side of
the unit. See Figure 68.
Figure 68: Dot plug location
Item Description
A Dot plug location
2. Insert at least 8 in. of 1/4 in. tubing into each
of these holes for sufficient penetration into
the air flow on both sides of the indoor coil.
Note: You must insert the tubes and hold
them in a position perpendicular to the
air flow so that velocity pressure does not
affect the static pressure readings.
3. Use an inclined manometer to determine the
pressure drop across the dry evaporator coil
and filters. The moisture on an evaporator
coil may vary greatly, measuring the pressure
drop across a wet coil under field conditions
could be inaccurate. To ensure that the coil is
dry, deactivate the compressors while the test
is being run.
Note: De-energize the compressors before
taking any test measurements to ensure
that the indoor coil is dry.
4. Use the pressure drop across a dry coil, to
determine the actual CFM through the unit
from the curve in the following figure.
WARNING
Failure to properly adjust the total system air quantity
can result in extensive blower damage.
Figure 69: Indoor Coil (dry coil + std. 2-in. filters) pressure drop versus supply air CFM
Item Description
A Large cabinet (50 t)
B Small cabinet (35 t)
C Large cabinet (40 t)
D Small cabinet (27.5 t and 30 t)
Installation Manual: YORK
®
Sun
™
Select YV28 to YV50
82
Johnson Controls Ducted Systems
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