42 McQuay IM 987
Mechanical Installation
Mixing Box (RAH 047C–077C only)
This section uses an outside air damper and a return air
damper. Using these dampers allows outside air to blend with
return air. Synchronized operation of the dampers is
accomplished by interconnecting rods. As one damper section
opens, the other section is closed. A total of 100% cfm is
always drawn from this section. Damper positioning can be
manually or automatically adjusted. With a field-installed
controller, automatic operation can be obtained.
These dampers provide a similar function to economizer
dampers. This option differs from an economizer in that no
unit mounted exhaust dampers are provided.
Note: For good airflow control, adjust linkages so damper
blades do not open beyond 70 degrees. Opening a
damper blade beyond 70 degrees has little effect on its
airflow. Do not “over close” low leak damper blades. The
edge seal should just lightly contact the adjoining blade.
The blades lock up if they are closed so far that the seal
goes over center.
Figure 48: Mixing Box
OA
CLOSED
OA
OPEN
90°
STROKE
.25" (6 mm)
.75"
(19 mm)
3.00"
(76 mm)
OA
CLOSED
OA
OPEN
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