Gosh, the air coming from my AC stinks. I have had this problem for a couple years now, just too lazy to get it fixed. Since it was a hot day today, me and a couple of female classmates hopped into my car to get some grub. Since they like AC instead of open windows, I turned it on. I was hoping that the smell wouldnt show up, but it did. It smelled like strong urine

WTF! I checked my air filter and everything looks fine, I looked all around my engine to see it there are any dead animals stuck in there, none. Whats the problem here?