So... According to AllData our Mustangs have an AC filter. I did not get my owner's manual with my car so referencing that is out. And I have yet to see it mentioned on the forum. It appears to be under the right side cowl... However I do not want to pull the cowl to find out if there is one. Has anyone seen or replaced one? How hard? How often does Ford recommend replacement? Thanks!

 

The term is a dust / pollen filter. It's located on the passenger side where you have to remove the cowl. Very easy to do. I change mine every 10,000, 15,000 miles depending on where you live.

 

Also commonly called a Cabin Air Filter. Once every 10K - 15K, like ThePope said above, is probably fine. You just pop the hood, undo 3 screws I think and then pull out the old filter, and replace with the new one. It's a tight fit but not hard.

 

You can download the owners manual for your car here:

https://owner.ford.com/servlet/Conte...e&ord=23587283

 

And install it with the filter in the correct direction! I reversed mine (once), and at highway speed, it vibrated (paper fins) to the point that I had to pull off the highway and correct it!