My pops had to move to a new office a few years ago (purchased a brand new office condo built to suit), and he called me about 6 months after moving in to ask if I'd go up in the attic space and change the filter in his air handler. I got up there, removed the access panel....and discovered there was no filter. Nice job, guys. It was installed by a contractor that I know, too. So we called and told them they needed to come clean the coil and install a filter. Supposedly they did.

Fast forward a year, and my Dad calls me again to change the filter for him. He had done it the previous couple of times, but I gave him a hard time for crawling around in the attic - he shouldn't be doing that. So I go up there again, remove the access panel...and this time discover a filter that is the correct width, but the incorrect height (too small), so air had been flowing right around the top of the filter. Ugh. After trying to install the correct size filter, I realized why the installer had used a smaller filter - whatever jackleg connected the return ductwork to the air handler had used long self-tapping screws that protruded so far into the slots that the filter slides into that they prevented the filter from clearing them, making it impossible to install the proper filter.

Once again, we called and told the installing contractor to come correct the issue. This time I met their field supervisor there and showed him exactly what was going on. Supposedly he had a crew come out and correct the problem, but I haven't been back up there to see it with my own eyes. I need to go check it out to make sure it's right.

Long story short - who knows what it could be, HokieGator. Hopefully you'll get a straight answer from the company you hire to repair it. Good luck.