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NOTE: De-energize the compressors before taking any test
measurements to assure a dry indoor coil.
Supply Air Drive Adjustment
The RPM of the supply air blower will depend on the required
CFM, the unit accessories or options and the static resistances
of both the supply and the return air duct systems. With this
information, the RPM for the supply air blower and the motor
pulley adjustment (turns open) can be determined from the
Blower Performance Data Tables.
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. Tighten blower pulley
and motor sheave set screws after these adjustments.
Re-checking set screws after 10-12 hours run time is
recommended.
Table 16: Additional Static Resistance
Size
Model
(Tons)
-15
(15)
XA
-20
(20)
1. Deduct these values from the available external static pressure shown in the respective Blower Performance Tables.
2. The pressure drop through the economizer is greater for 100% outdoor air than for 100% return air. If the resistance of the
return air duct is less than 0.25 IWG, the unit will deliver less CFM during full economizer operation.
Johnson Controls Ducted Systems
1, 2
CFM
Economizer
4500
0.10
6000
0.10
7500
0.10
6000
0.10
7500
0.10
9000
0.15
10000
0.15
For the XA-15 Model, high speed drive accessory 1LD0413
(containing a smaller blower pulley and a shorter belt) is
available for applications requiring the supply air blower to
produce higher CFM's and/or higher static pressures. Note the
following:
1.
The supply air CFM and external static pressure must be
within the limitations shown in the Blower Performance
Tables 11 and 12.
2.
Pulleys can be adjusted in half turn increments.
3.
The tension on the belt should be adjusted as shown in the
Belt Adjustment, Figure 17.
4.
Tighten blower pulley and motor sheave set screws after
any adjustments. Re-check set screws after 10-12 hours
run time recommended.
Electric Heat kW
18
36
0.10
0.10
0.10
0.10
0.10
0.20
0.10
0.10
0.10
0.20
0.10
0.30
0.15
0.35
5168274-BIM-I-1121
1
54
72
0.20
0.20
0.20
0.20
0.30
0.40
0.20
0.20
0.30
0.40
0.40
0.60
0.55
0.75
35
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