Maybe I missed it. But I didn't see in your posts if you had checked your filter? It could be plugged up w/dirt. For a commercial package type unit, there should be 1 inside filter and maybe one outside in the unit. Inside one's at your return air grill (you may already know all of this). The outside one, if there is one, usually has a service panel on the unit marked w/filter change dates or filter size. I used to work as a dispatcher for a large AC company in Austin, and we saved people many a service call by having them check this first.

Cory