Mammoth 800 to 5500 CFM: Dedicated Outdoor Air System with Enthalpy Wheels (VHC) - Manual (Page 17)

MAMM-VHC-IOM-1A (JANUARY 2013) 17
Disconnect the four-wire service connector between the
motor and the VFD (#1, Figure 7). Remove the four bolts
(#2, Figure 7) and slide the motor and plenum fan past the
inlet cone, then lift out of the unit. A 1¾” socket is required
to remove the fan from the motor shaft.
Plenum Fan and Motor Removal
WARNING
No lubrication is necessary during servicing.
!
1. Measure the belt span with a span scale (see Figure
6).
2. Divide the belt span by 64 to determine the belt deflec-
tion needed to check tension.
3. Set the O-ring on the span scale to the required de-
flection value.
4. Set the small O-ring at zero on the force scale.
5. Place the scale end of the tension checker squarely
on one belt at the center of the belt span. Apply force
on the plunger until the bottom of the large O-ring is
even with the top of the next belt or until it is even with
a straight edge laid across the sheaves.
6. Read the force scale under the small O-ring to
determine the force required to give the needed
deflection.
7. Compare the force scale reading in Step 6 with the
correct value for the belt style and cross section. The
force scale reading should be between the minimum
and maximum values shown in Table 2.
8. If the deflection value is below the minimum, tighten
the belts. If the deflection value is above the maxi-
mum, loosen the belts. The tension on new belts
should be checked during the first day of operation, at
the end of the first week and monthly thereafter.
Belt Tension Adjustment
WARNING
Disconnect the main power switch to the unit before per-
forming service and maintenance procedures.
!
Plunger with
deflection force scale (lbs)
Body with deflection
distance scale (inches)
Small O-ring Large O-ring
Force
Deflectio
n
Belt Span
Figure 6: Belt tension adjustment
Table 2: Recommended Deflection Force
V-belt
Cross
Sec-
tion
Small
Sheave
Diameter
Range
Recommended Deflection Force
(lbs)
Initial
Installation
Re-tensioned
Maximum Minimum
A
3.0” to 3.4” 3.3 2.9 2.2
3.6” to 4.2” 3.5 3.1 2.4
4.6” to 6.0” 3.7 3.3 2.5
B
4.6” to 5.4” 6.0 5.1 4.0
5.6” to 7.4” 6.3 5.5 4.2
8.6” to 9.4” 6.6 5.7 4.4