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Minimum Damper Position Range
The motorized outdoor air damper operation is optimized
as shown in the shaded area of Chart 2. Unit operation
during minimum damper position above this curve
increases the potential for rain being drawn into the unit.
1- Remove the metal mesh filter from the hood.
Measure the static pressure differential between the
return compartment (through filter door is
recommended) and outside the unit. Operate the
unit with the damper open to minimum position.
Record the single blower speed pressure differential
in table 2.
2-
Units With More Than One Blower Speed -
Repeat the static pressure measurement at each
blower speed and minimum set point combination.
Record the multiple blower speed pressure
differential in table 2.
3- Read the damper percentage open.
Units Equipped With Unit Controller -
The damper percentage open was entered into the
Unit Controller.
Units Not Equipped With Unit Controller -
Operate the unit with the damper open to minimum
position. Measure the voltage between pins 7 and 9
from the damper motor plug P4. Calculate the
percentage open from the formula:
% Open = [(Measure voltage - 2.5) / 7.0] X 100
4- Plot the damper % open and static pressure drop on
Chart 2.
5- Replace the metal mesh filter.
TABLE 2
Single Blower Speed
Multiple Blower Speed
Static Pressure Differential - “w.c.
Damper % Open
Static Pressure Differential - “w.c.
Damper % Open
CHART 2
OPTIMAL OUTDOOR AIR OPERATION
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
Measured Static Pressure Drop Across Damper (inch w.c.)
Estimated Airflow Through Damper (CFM)
25%
52%
38%
73%
66%
80%
100%
59%
