A layer of dust that was thick

I have a close friend who is legitimately bad about cleaning his apartment.  After his lady broke up with him several months ago, he has been a wreck. He doesn’t shower much, he has clothes piling up in the corners on the floor, and I don’t think he has mopped or vacuumed once since she left.  His home is starting to smell and I told my friend that he needs to clean up or I’m not coming to his home anymore. He impressed me and spent a few weeks slowly chipping away at the whole mess and when he was finally done the place looked fantastic.  However, the smell from before he cleaned was still lingering a little ands that’s when I thought to ask him if he had changed the a/c filter. He looked at me shocked for a moment and then ran over to his closet. I asked him if everything was okay and that’s when he told me that he realized that he hadn’t even checked the filter once in the last several months.  He pulled it out of the air handler and the two of us looked at it in collective horror. I have never seen a dirtier AC filter in my entire life and I hope I never do. The layer of dirt and grime collected inside was so thick that you could no longer make out the grooves in the filter itself, it was just 1 immense grayish brown mass. My friend purchased a new filter and cleaned out the plan a little with some water and vinegar and now his house smells wonderful.  He said that his electric bill dropped too since his a/c isn’t working as hard to keep up anymore. Thankfully nothing broke inside the unit because of the neglect.

air quality