I had a problem with my a/c stinking everytime I turned it on and thought I'd share my solution as I've noted I'm not the only one to complain of this issue

my 95 mecurey gm had the same problem

no amount of a/c system spray cleaner / deodorizer is going to help you
- that stuff even gives me headaches

the solution was simple as it turned out and I've now had 5 summers without the a/c stinking like cow poo

some time ago I bought one of "street scene's" smooth cowel top
a simple kinda cheep hunk of fiberglass that replaces the factory black plastic cowel vents with a smooth ventless cover

I installed it in the fall and to my suprise every summer since then my a/c stink is gone
simple solution , keep the rain outta the cowel

as for the smell of cow poo - it's gone , compleately and totally and has been gone now for the fifth summer in a row