Summary problem: Air flow from coming from the AC unit in the attic.

Description: I have a split central air unit - one for the first floor and another for the 2nd floor. The second floor's unit has the compressor outside. The air handler and evaporator and associated duct work is in the attic.

I was up in the attic adjusting the air flow between the ducts to the various rooms to accommodate the summer heat when I noticed that there was airflow coming from the general area between the air unit and the evaporator. Is that normal? I thought that the unit in the attic is supposed to be sealed.

A year or so ago I had the evaporator unit in the attic replaced - I'm wondering if some of the work they did created an air leak.

Any experts with advice?