Inspection today had a return of one of the units place on the exterior. Both units were 5 year old Trane. Any particular reason why they would do that?
Also, what are your thoughts on the drip leg?
Wrong , needs to be repaired
I see nothing wrong with that fresh air make-up to the R/A assuming it has a damper. On the other hand, that gas line sediment trap results in a snicker.
Here’s a discussion on fresh-air intakes.
This is Texas Roy! 
Bill, if you don’t know what your looking at, maybe you should leave it alone?..
Perhaps not the most elegant install but okay if filtered and able to close when not running.
Quite possibly source of outdoor air. Helps to reduce stale air, and a source of makeup air exhausted by kitchen and bath fans. Filtration would take place at the AHU, same as the rest of the return air.
Common (and required in some places) in commercial applications. Would want to see at least a fixed damper to allow balancing, but can be closed when not in use by a barometric damper, or a motorized damper with a CO2 monitor.
Thanks guys, and thanks Mike for the link!
Davey, who’s Bill?
BTW, the drip/dirt leg is wrong, it wouldn’t trap much of anything set up that way. The device should change flow of fuel 90 degrees and the tee/leg post direction change.
Nothing wrong with the return air to the outside.
It is acceptable to connect the furnace combustion make up air source to the cold air return.
Edit:This is with a unit in the attic space, something I never see in my area, so my comment is for a heating unit withing a controlled area.
You boys from the South will have to explain what is proper to us Yankees.