5326602-XIM-B-1019
Johnson Controls Ducted Systems
41
Air Balance
Start the supply air blower motor. Adjust the resistances in both
the supply and the return air duct systems to balance the air
distribution throughout the conditioned space. The job
specifications may require that this balancing be done by
someone other than the equipment installer.
Checking Air Quantity
Method One
1.
Remove the dot plugs from the duct panel (for location of
the dot plugs see Figures 12 and 13).
2.
Insert eight-inches of 1/4 inch metal tubing into the airflow
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 pressure
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, measuring
the pressure drop across a wet coil under field conditions
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 29. In order to obtain an accurate measurement, be
certain that the air filters are clean.
5.
To adjust Measured CFM to Required CFM, see SUPPLY
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
perpendicular 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.
Table 24: Indoor Blower Specifications
Size
(Tons)
Model
Motor
Motor Sheave
Blower Sheave
Belt
HP
RPM
1
1. 1725 RPM at 60 Hz.
Eff.
SF
Frame
Datum Dia.
(In.)
Bore (In.) Model
Datum Dia.
(In.)
Bore (In.)
Model
120
(10)
ZF
2
1425
0.8
1.15
56
3.4 - 4.4
7/8
1VM50
7
1
AK74
A54
4
1455
0.87
1.15
184T
4.0 - 5.0
1-1/8
1VP56
6.2
1
AK66
A56
150
(12.5)
ZF
4
1455
0.87
1.15
184T
4.3 - 5.3
1-1/8
1VP56
6.6
1
BK72
BX56
Table 25: Power Exhaust Specifications
Model
Voltage
Motor
Motor
Fuse Size
CFM @
0.1 ESP
HP
RPM
1
1. Motors are multi-tapped and factory wired for high speed, suitable for 50 HZ power supply
QTY
LRA
FLA
MCA
2PE04703246
460-1-60
3/4
1075
1
3.4
2.2
2.8
5
3800
Belt drive blower systems MUST be adjusted to the
specific static and CFM requirements for the application.
The Belt drive blowers are NOT set at the factory for any
specific static or CFM. Adjustments of the blower speed
and belt tension are REQUIRED. Verify proper sheave
alignment; tighten blower pulley and motor sheave set
screws after these adjustments. Re-checking set screws
after 10-12 hrs. run time is recommended.
Failure to properly adjust the total system air quantity
can result in extensive blower damage.
