Reefer guy here but saw this and it interested me. The first 2 pics are one unit and the second 2 pics are another unit. That PVC goes to a smoke detector inside the blower compartments and, as you can see, the pipe terminates at the drains. There is an additional smoke detector in the blower areas that are tubed the way I'm used to seeing them. What is being accomplished here??
In the first two pictures, the lines connected on the back side of the unit aren't even serving as a drain.
I've got no ideas except for the installer had extra PVC and didn't know what to do with it - or it's a means to equalize the pressure in the condensate line to eliminate a trap.
on a 100F day and a bird lands on top of the PVC riser pipes...snap the manufacturers spend millions of dollars keeping units weather tight. if any PVC is on the negative side of that supply fan they are going to suck rain water into the ducts... the typical trap is right below the fan access panel or coming out from the below that OA hood..that is a power exhaust for sure...maybe that's the piping show needed
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It`s better to be silent and thought the fool; than speak and remove all doubt. 
the manufacturers spend millions of dollars keeping units weather tight. if any PVC is on the negative side of that supply fan they are going to suck rain water into the ducts... the typical trap is right below the fan access panel or coming out from the below that OA hood..that is a power exhaust for sure...maybe that's the piping show needed
