Expansion Valve Superheat Adjustment
It is very important that the expansion valve superheat setting
be adjusted to be between 10°F (5.5°C) and 13°F (7.2°C).
Insufficient superheat will cause liquid floodback to the
compressor which may result in slugging. Excessive superheat
will reduce system capacity and shorten compressor life.
Turn the adjustment stem clockwise to increase superheat.
Not exceeding one turn, adjust the stem and then observe the
superheat. Allow up to 30 minutes for the system to rebalance
at the final superheat setting.
Checking Superheat
Following are recommendations for checking superheat:
1 .
Close the unit section doors. Running the unit with
its doors open will affect expansion valve and system
operation considerably.
2 .
Check the pressure and temperature at the suction
gauge port.
Sheave Alignment
1 .
Verify both motor and fan sheaves are in alignment
and the shafts are parallel. The center line of the motor
sheave must be in line with the center line of the fan
.
2 .
Verify that all setscrews are torqued to the values shown
before starting drive. Check
setscrew torque and belt tension after 24 hours of service.
Figure 80: Sheave Alignment (Adjustable Shown)
Drive Belt Tension Adjustment
1 .
The ideal tension is the lowest tension at which the belt
will not slip under peak load conditions. Over tensioning
shortens belt and bearing life.
2 .
Check tension frequently during the first 24–48 hours of
operation .
3 .
Keep belts free from foreign material which may cause
slippage.
4 .
Make V-drive inspection on a periodic basis. Adjust
tension if the belt is slipping. Do not apply belt dressing.
This may damage the belt and cause early failure.
Air Balancing
The following should be performed by a qualified air balancing
technician:
1 .
Check the operating balance with the economizer
dampers positioned for both full outdoor air and minimum
outdoor air .
2 .
Verify that the total rflow will never be less than that
required for operation of the electric heaters or gas
furnace.
3 .
When the final drive adjustments or changes are
complete, check the current draw of the supply fan
motors. The amperage must not exceed the service
factor stamped on the motor nameplate.
WARNING
Moving machinery hazard . Can cause severe personal
injury or death .
Do not use a mechanically driven tachometer
to measure the speed return fans on this fan arrangement.
Use a strobe tachometer.
Rotating parts can cause severe personal injury or death .
Replace all belt/fan guards that are removed for service.
Bearing
Motor
Must be
parallel
Fixed Pitch
Sheave
Center lines
must coincide
Must be
parallel
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95
IM 1058-8 • MAVERICK II ROOFTOP SYSTEMS
