Blower/Motor Adjustment - Modine MDB Série Manuel D'installation Et De Maintenance

start-uP Procedure
Steps 34-35 must be performed on LOW SPEED if unit is equipped
with a VFD. If the unit does not have a VFD, proceed to step 36.
34. Adjust the VFD speed to the low speed setting and the
temperature controls to force the unit to high fire.
35. Observe the pressure indicated on the "U" tube manometer
and adjust the manifold pressure by adjusting the low speed
input potentiometer (MP-02) and NOT the gas valve regulator.
Adjust the pressure to match the low speed manifold pressure
on the unit serial plate. The flame will be approximately 10 to
12" in length and may be yellow in color.
36. With the unit off, close the main gas manual hand valve.
Remove the "U" tube manometer and replace the 1/8" pipe
plug test port at the burner.
multi-speed and return air units
Units with VFD's or return air options require the following
additional start-up checks.
two-speed units (vFd)
1. Check the motor and blower speed at both high and low speed.
2. Check motor amps at both high and low speed.
vFd Building Pressure control
Check to make sure the building pressure control is operating
properly. The building pressure control is designed to decrease
or increase motor and blower speed as building pressure
increases or decreases.
To check if this is occurring, turn on an exhaust fan and observe
the motor speed. The motor speed should increase. The VFD
display will also indicate that the frequency (Hz) is increasing.
With all exhaust fans operating (maximum exhaust fan load), the
VFD will continue to increase blower speed toward full speed to
meet the building pressurization requirements.
return air units (Not available in Canada)
70/30, 75/25 return air units
1. Check to make sure that the outside air burner by-pass damper
and return air damper operate correctly and without binding.
2. Check the position of the by-pass and return air damper
based on the mode of operation in Table 21.1.
75/25 Building Pressure control return air units
(Not available in Canada)
1. Check to make sure that the outside air burner by-pass damper
and return air damper operate correctly and without binding.
2. Check to make sure the building pressure control is
operating correctly.
The building pressure control is designed to change the
position of both the outside air and return air-mixing dampers
as the pressure in the building increases or decreases.
To check if this is occurring, turn on an exhaust fan and observe the
return air damper position. It should start to close. Turn on additional
exhaust fans. The return air damper should close further.
With all of the exhaust fans operating (maximum exhaust load)
the return air damper should be in the fully closed position, and
the burner by-pass damper should be in the fully open position
(see Table 21.1).
table 21.1 - outside air Bypass - return air damper
Positions
mode By-Pass Damper
100% outside air
Open
With return air Closed
damper Positions
Return Air Damper
Closed
Open
Final step
After all of the initial start-up procedures have been performed,
the unit is ready for commissioning. Set the temperature controls
for automatic operation if the unit is to be put into service
immediately. If the unit is to be left for stand-by operation, set the
optional Summer/Off/Winter switch to the "Off" position and turn
the electric power to the unit off at the unit's disconnect switch.

Blower/motor adjustment

Units are supplied with adjustable drive sheaves. All units are
supplied with an adjustable motor mounting plate.
Follow electrical connections for supplying power to the motor.
Check for the proper blower rotation. The correct direction of
rotation is marked on the blower housing. Start blower and
check blower speed (rpm) using a hand-held tachometer
(strobe-type, or reflective-type tachometer are preferred types).
Measure the unit air volume being delivered and compare to
the rated air volume on the unit serial plate. If the measured air
volume does not match, adjust the fan RPM by adjusting the
sheave on the motor (refer to Figure 21.1) as follows:
a. Loosen motor base and take belt(s) off of the motor sheave.
b. Loosen set screw(s) on the outer side of the adjustable motor sheave.
c. To speed up the blower, turn the outer side of the drive sheave
clockwise to close the pulley. To slow the blower speed, turn
the outer side of the adjustable sheave counterclockwise to
open the pulley. If proper air flow and/or blower speed cannot
be obtained, contact the factory for alternate drive selections.
d. Retighten motor sheave set screw(s) and replace belt.
e. Motor base may have to be shifted to obtain proper belt
tension. The proper belt tension is achieved when there is
a 3/4" deflection of the belt when a force of approximately 5
pounds is applied to the center of the belt using a belt tension
gauge. DO NOT OVER TIGHTEN! (see Figure 21.2).
f. Recheck blower speed and air volume delivered after
adjustment. Repeat steps until air volume matches the
rated air volume on the unit serial plate.
g. Check motor amps to make sure the actual motor amp
draw does not exceed the motor nameplate amp draw.
Figure 21.1 - Blower and motor drive assembly
2
1. Drive Belt
2. Blower Sheave
3. Motor Sheave
Figure 21.2 - Belt tension adjustment
3/4" deflection with 5 lbs. of force
7-500.10
6
1
5
4. Belt Tension Adjusting Screw
5. Motor Base Fastening Bolts
6. High Temperature Limit Control
3
4
21