12 IM709
Return Air
Air return to the unit can be arranged in different ways.
1. Ducted return
Return ductwork may be attached to the 2" flange around the
perimeter of unit's return air opening (refer to Figure 12).
Use a canvas type duct connecting collar. All ductwork con-
nected to the unit should be of adequate size and construc-
tion for the application. A canvas type connector is also
recommended where the duct penetrates the machine room
wall(s). This will help prevent vibration generated by air
movement in the duct from being transmitted out to the
occupied spaces.
Note: Do not obstruct unit access panel located below the
return opening.
Note: For units with ducted return, connect the open port
on the clogged filter switch (PC5) to the return air
duct.
2. Free return
The mechanical equipment room may be used as a return
plenum with no hard connection at the unit.
Note: Some building codes do not allow the use of the
mechanical room as a return plenum. Check appli-
cable local codes for each installation.
Figure 12. Return duct connections
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