Page 20
LGH/LCH420, 480, 540, 600
B-Check Belt Tension
Overtensioning belts shortens belt and bearing life. Check
belt tension as follows:
1-Measure span length X. See figure 28.
MEASURE BELT TENSION
FIGURE 28
DEFLECTION 1/64” PER INCH OF SPAN
OR 0.4mm PER 25.4mm OF SPAN
FORCE
2-Apply perpendicular force to center of span (X) with
enough pressure to deflect belt 1/64” for every inch of
span length or 0.4mm per 25.4mm of span length.
Example: Deflection distance of a 40” span would be
40/64” or 5/8”.
Example: Deflection distance of a 1016mm span would
be 16mm.
3-Measure belt deflection force. Used belt values apply
when tightening the belt after 24-48 hours.
For a used belt, the deflection force should be:
5 lbs. for 5 & 7.5 HP applications
8 lbs. for 10 & 15 HP applications
7 lbs. for 20, 25, & 30 HP applications
For a new belt, the deflection force should be:
8 lbs. for 5 & 7.5 HP applications
12 lbs. for 10 & 15 HP applications
11 lbs. for 20, 25, & 30 HP applications
A force below these values indicates an
undertensioned belt. A force above these values
indicates an overtensioned belt.
C-Blower Operation
Initiate blower only (G) demand at thermostat according to
instructions provided with thermostat. Unit will cycle on
thermostat demand. The following steps apply to
applications using a typical electro-mechanical thermostat.
1- Blower operation is manually set at the thermostat
subbase fan switch. With fan switch in ON position,
blowers will operate continuously.
2- With fan switch in AUTO position, the blowers will cycle
with demand. Blowers and entire unit will be off when
system switch is in OFF position.
C-Determining Unit CFM
1- The following measurements must be made with a dry
indoor coil. Run blower (G demand) without a cooling
demand. Measure the indoor blower shaft RPM. Air
filters must be in place when measurements are taken.
2- With all access panels in place, measure static
pressure external to unit (from supply to return). Blower
performance data is based on static pressure readings
taken in locations shown in figure 29.
3- With all access panels in place, measure static
pressure external to unit (from supply to return). Blower
performance data is based on static pressure readings
taken in locations shown in figure 29.
Note - Static pressure readings can vary if not taken where
shown.
FIGURE 29
LOCATION OF STATIC PRESSURE READINGS
SUPPLY AIR
READING
LOCATION
SUPPLY
RE
TURN
INSTALLATIONS WITH DUCTWORK
SUPPLY
RE
TURN
INSTALLATIONS WITH CEILING DIFFUSERS
MAIN
DUCT RUN
FIRST BRANCH
OFF OF MAIN RUN
DIFFUSER
ROOFTOP UNIT
ROOFTOP UNIT
SUPPLY AIR
READING
LOCATION
RETURN AIR
READING LOCATION
RETURN AIR
READING
LOCATION
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