What does the code AF on my whirlpool cabrio dryer mean?

The AF indicates an insufficient air flow.

If you type your question into a Google search, you will find that this is a VERY COMMON problem with this particular model. There are posts all over the web about it.

Good luck with it!

Clean your dryer ventilation ducts (not just the ends)! I did this today after seeing "AF" for a year on my dryer. The "AF" has disappeared and my laundry dried in 25-30 minutes instead of the 3 hours it had been taking.

If you take your leaf blower and tape it to the duct in the wall ,turn it on high all the trapped lint will blow out, it takes a while, and you will litter the neighborhood with lint, so do it at night this will fix the problem without paying someone!

That's assuming the bloke attaches while indoors and vents outward. LOL