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882108-YIM-B-1012
60 Johnson Controls Unitary Products
CHECKING AIR QUANTITY
1. Remove the dot plugs from the two 5/16 inch holes in the
blower motor and the filter access doors.
2. Insert at least 8 inch of 1/4 inch metal 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 or other high resolution
pressure measurement device, determine the pressure
drop across a dry evaporator coil. Since the moisture on
an evaporator coil may vary greatly, measuring the pres-
sure drop across a wet coil under field conditions would
be inaccurate. To assure a dry coil, the compressors
should be de-activated while the test is being run.
4. Knowing the pressure drop across a dry coil, the actual
CFM through the unit with clean 2 inch filters, can be
determined from the curve in Figure 52 and 53.
NOTE: De-energize the compressors before taking any test
measurements to assure a dry evaporator coil.
After readings have been obtained, remove the tubes and
reinstall the two 5/16 inch dot plugs.
It is especially important to limit the rpm of the fan in VFD-
bypass-equipped units; it may be tempting to set max rpm in
the VFD to less than 60 Hz - but the bypass will go to 60 Hz
immediately on activation.
On VAV and VFD units be certain all IGV’s on VAV
unit are full open, VFD drive is set to maximum
output, exhaust dampers are closed and individual
space damper boxes are full open.
VFD units with bypass must not have the bypass
activated unless all individual space dampers are
full open.
TABLE 38: BELT ADJUSTMENT
FAN MOTOR HORSE POWER 5 7.5 10 15 20 25
30 TON FORWARD CURVED SUPPLY FAN SIZE: 22 X 20
Belt Deflection Force (lbs) new belts - - 10.5 12.6 15.2 22.1
Belt Deflection Force (lbs) old belts - - 7.1 8.5 10.2 14.8
40 TON FORWARD CURVED SUPPLY FAN SIZE: 25 X 20
Belt Deflection Force (lbs) new belts - - 10.5 12.6 15.2 15.2
Belt Deflection Force (lbs) old belts - - 7.1 8.5 10.2 10.2
30 & 40 TON POWER EXHAUST FAN SIZE: (2) 15 X 15
Belt Deflection Force (lbs) new belts - 7.9 9.4 9.4 - -
Belt Deflection Force (lbs) old belts - 5.3 6.3 6.3 - -
25 TON FORWARD CURVE SUPPLY FAN SIZE: 22 X 20
New Belt - 10.5 10.5 12.6 15.2 -
Old Belt - 7.1 7.1 8.5 10.2 -
25 TON POWER EXHAUST
New Belt 10.5 10.5 12.6 - - -
Old Belt 7.1 7.1 8.5 - - -
Failure to properly adjust the total system air quan-
tity can result in extensive blower or duct damage.