44 McQuay IM 937
System Check, Test, and Start
Drive Sheave Alignment
Check the drive sheave alignment using the four-point method
shown in Figure 42. When measuring from the straight edge to
the belt, the distance at points A, B, C, and D must be equal for
correct alignment.
Figure 42: Drive Alignment
Drive Belt Adjustment
General rules of tensioning
• The ideal tension is the lowest tension at which the belt will
not slip under peak load conditions.
• Check tension frequently during the first 24–48 hours of
operation.
• Overtensioning shortens belt and bearing life.
• Keep belts free from foreign material that can cause
slippage.
• Make V-drive inspections on a periodic basis. Adjust the
tension if the belt is slipping. Do not apply belt dressing.
This can damage the belt and cause early failure.
Tension measurement procedure
1 Measure the belt span. See Figure 43.
2 Place the belt tension checker squarely on one belt at the
center of the belt span. Apply force to the checker,
perpendicular to the belt span, until the belt deflection
equals belt span distance divided by 64. Determine force
applied while in this position.
3 Compare this force to the values on the drive kit label
located on the fan housing.
Figure 43: Drive Belt Adjustment
When new belts are installed, the initial tension drops. After 48
hours of operation, check the tightness of all setscrews on the
fan hub and bearing sleeves and retighten belts.
Note: If after all tension adjustments the belts slip or squeal
when starting, increase tension slightly. Replace the
belts if they are worn or glazed.
Final Control Settings
When all of the start-up procedures are completed, set the
individual control parameters for operation, as follows:
• Unit switch S7 to AUTO
• Heating/Cooling control parameters, as required
• Alarm limits, as required
• Night setback parameters, as required
• Duct static pressure and building static pressure, as required
• Economizer control parameters, as required
• Control timers. as required
• Date and time, as required
• Operating schedule, as required
• Holiday schedule, as required
Note: For the keypad menu structure, see OM 920.
Maintaining Control Parameter Records
After the unit is checked, tested, and started and the final
control parameters are set, record the final settings and keep
them on file. Update this file whenever changes are made to
the control parameters. This facilitates any required analysis
and troubleshooting of the system operation.
AB
C
D
FIELD SUPPLIED STRAIGHTEDGE
B e l t S p a n
D e f l e c t i o n =
B e l t S p a n
6 4
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