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Phasing
Ducted Systems Model XA units are properly phased at the
factory. Check for proper compressor rotation. If the blower or
compressors rotate in the wrong direction at start-up, the
electrical connection to the unit is misphased. Change the
phasing of the Field Line Connection at the factory or field
supplied disconnect to obtain proper rotation. (Scroll
compressors operate in only one direction. If the scroll is
drawing low amperage, has similar suction and discharge
pressures, or producing a high noise level, the scroll is
misphased.)
Scroll compressors require proper rotation to operate
correctly. Units are properly phased at the factory. Do
not change the internal wiring to make the blower
condenser fans, or compressor rotate correctly.
Blower Rotation
Check for proper supply air blower rotation. If the blower is
rotating backwards, the line voltage at the unit point of power
connection is misphased (See 'PHASING').
Belt Tension
The tension on the belt should be adjusted as shown in Figure 17.
(A)
Figure 17: Belt Adjustment
Johnson Controls Ducted Systems
Defl Force
(B)
*Never Loosen
(C)*
Procedure for adjusting belt tension:
1. Loosen four nuts (top and bottom) A.
2. Adjust by turning (B).
3. Never loosen nuts (C).
4. Use belt tension checker to apply a perpendicular
force to one belt at the midpoint of the span as
shown. Deflection distance of 4mm (5/32") is
obtained.
To determine the deflection distance from normal
position, use a straight edge from sheave to sheave as
reference line. The recommended deflection force is as
follows:
Tension new belts at the max. deflection force
recommended for the belt section. Check the belt
tension at least two times during the first 24 hours of
operation. Any retensioning should fall between the min.
and max. deflection force values.
5. After adjusting re-tighten nuts (A).
CFM Static Pressure and Power-Altitude and Temperature
Corrections
The information below should be used to assist in application of
product when being applied at altitudes at or exceeding 1000
feet above sea level.
The air flow rates listed in the standard blower performance
tables are based on standard air at sea level. As the altitude or
temperature increases, the density of air decreases. In order to
use the indoor blower tables for high altitude applications,
certain corrections are necessary.
A centrifugal fan is a "constant volume" device. This means
that, if the rpm remains constant, the CFM delivered is the
same regardless of the density of the air. However, since the air
at high altitude is less dense, less static pressure will be
generated and less power will be required than a similar
application at sea level. Air density correction factors are shown
in Table 10 and Figure 18.
5168274-BIM-I-1121
29
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