16
motor and bearing failure will occur. Check you belt
drive for adequate “run-in” belt tension by measuring the
force required to deflect the belt at the midpoint of the
span length. Belt tension force can be measured using
a belt tension gauge, available through most belt drive
manufacturers.
S
P
AN LEN
GTH
t
*DEFLEC
TI
ON
FORCE
h
C
d
H
D
*Apply force to the center of the span.
BELT TENSION ADJUSTMENT
t = Span length, inches
C = Center distance, inches
D = Larger sheave diameter, inches
d = Smaller sheave diameter, inches
h = Deflection height, inches
BELT DRIVE
USED
NEW
AX
Standard
3.0 to 4.0 4.2 ± 0.5 5.5 ± 0.5
0.313
DEFLECTION
FORCE (lbs)
TYPE
DEFLECTION
(in)
SMALL
SHEAVE
DIAMETER
(in)
RECOMMENDED POUNDS OF FORCE PER BELT
New V-belts will drop rapidly during the first few hours of
use. Check tension frequently during the first 24 hours
of operation. Tension should fall between the minimum
and maximum force. To determine the deflection distance
from a normal position, measure the distance from
sheave to sheave using a straightedge or a cord. This is
your reference line. On multiple belt drives, an adjacent
undeflected belt can be used as a reference.
MOTOR SHEAVE ADJUSTMENTS
Vl, Vm, & 2vp Variable Pitch Key Type Motor
Sheaves
The driving and driven motor sheaves should be in
alignment with each other and the shafts parallel.
Vl & Vm Sheaves Adjustment
1. Loosen set screw “B” using a 5/32” Allen key.
2. Making half or full turns from closed position, adjust
sheave pitch diameter for desired speed. DO NOT
OPEN MORE THAN FIVE FULL TURNS.
3. Tighten set screw “B” securely over flat.
4. Carefully put on belts and adjust belt tension. DO
NOT FORCE BELTS OVER GROOVES.
5. Ensure all keys are in place and the set screws tight
before starting drive. Recheck set screws and belt
tension after 24 hours service.
NOTE:
Future adjustments should be made by loosening
the belt tension and increasing or decreasing the pitch
diameter of the sheave by half or full turns as required.
Readjust belt tension before starting drive.
C
B
VL & VM
NOTE:
Do NOT operate sheave with flange projecting
beyond the hub end.
Electrical Input Check
Make preliminary check of evaporator fan ampere draw
and verify that motor nameplate amps are not exceeded. A
final check of amp draw should be made upon completion
of air balancing of the duct system (see Appendix B).
GAS SYSTEM CHECK
Pre-Operation Checks
1. Close the manual gas valve external to the unit.
2. Turn off the electrical power supply to the unit.
3. Change heating setpoint to its lowest possible setting.
4. Remove the heat exchanger door on the side of the
unit by removing screws.
5. This unit is equipped with an ignition device which
automatically lights the main burner. DO NOT try to
light burner by any other method.
6. Move the gas control valve switch to the OFF position.
7. Wait five minutes to clear out any gas.
8. Smell for gas, including near the ground. This is
important because some types of gas are heavier
than air. If you have waited five minutes and you do
smell gas, immediately follow the warning WHAT TO
DO IF YOU SMELL GAS on page 2 of this manual.
If having waited for five minutes and no gas smell is
noted, move the gas control valve switch to the ON
position.
9. Replace the heat exchanger door on the side of the
unit.
10. Open the manual gas valve external to the unit.
11. Turn on the electrical power supply to the unit.
12. Change heating setpoint to desired setting.
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