Supply air drive adjustment
CAUTION
Before making any blower speed changes review
the installation for any installation errors, leaks or
undesirable systems effects that can result in loss
of airflow.Even small changes in blower speed can
result in substantial changes in static pressure and
BHP. BHP and AMP draw of the blower motor will
increase by the cube of the blower speed. Static
pressure will increase by the square of the blower
speed. Only qualified personnel should make blower
speed changes, strictly adhering to the fan laws.
At unit start-up, the measured CFM may be higher
or lower than the required CFM. To achieve the
required CFM, the speed of the drive may have
adjusted by changing the datum diameter (DD) of
the variable pitch motor sheave as described below:
Use the following tables and the DD calculated per
the above equation to adjust the motor variable
pitch sheave.
EXAMPLE NEW DATUM DIAMETER
A 4 ton unit was selected to deliver 1,600 CFM with a
1VL34 motor sheave, but the unit is delivering 1,350
CFM. The variable pitch motor sheave is set at 4
turns open.
Use the equation to determine the required DD for
the new motor sheave,
Use Table 54 to locate the DD nearest to 2.48 in.
Close the sheave to 2 turn open.
EXAMPLE NEW BHP
= (Speed increase)
3
• Original BHP = New BHP
= (Speed increase)
3
• BHP at 1,350 CFM
EXAMPLE NEW MOTOR AMPS
= (Speed increase)
3
• Original Amps = New Amps
= (Speed increase)
3
• Amps at 1,350 CFM
Table 54: Motor Sheave Datum Diameters
1VL34 1VL44 1VP50 1VP56
Turns Open Datum Diameter Turns Open Datum Diameter Turns Open Datum Diameter Turns Open Datum Diameter
0 2.9 0 3.8 0 4.4 0 -
1/2 2.8 1/2 3.7 1/2 4.3 1/2 -
1 2.7 1 3.6 1 4.2 1 5.3
1-1/2 2.6 1-1/2 3.5 1-1/2 4.1 1-1/2 5.2
2 2.5 2 3.4 2 4.0 2 5.1
2-1/2 2.4 2-1/2 3.3 2-1/2 3.9 2-1/2 5.0
3 2.3 3 3.2 3 3.8 3 4.9
3-1/2 2.2 3-1/2 3.1 3-1/2 3.7 3-1/2 4.8
4 2.1 4 3.0 4 3.6 4 4.7
4-1/2 2.0 4-1/2 2.9 4-1/2 3.5 4-1/2 4.6
5 1.9 5 2.8 5 3.4 5 4.5
5-1/2 - 5-1/2 - 5-1/2 - 5-1/2 4.4
6 - 6 - 6 - 6 4.3
CAUTION
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 and belt tension after 10-12
hrs. run time is recommended.
INSTALLATION MANUAL ZY SERIES 3-10ton 60 Hertz R-410A98
Johnson Controls Ducted Systems
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