In what situations would a 3 ton airhandler be installed with a 2.5 compressor? I had started a thread yesterday regarding my parents AC which is set up this way but was wondering if anyone can clarify why a contractor would have done this and if it safe or efficient or technically correct to do.

Also, can it be done the other way? ie.) 2.5 air handler with a 3 ton compressor?

Thanks again for all the advice. This is a great site.