How to remove a decomposing animal odor from AC unit

What is your question?

Not sure what crawled up into my AC unit but it’s truly foul. How do I find out what it is and remove it?

What makes this problem better or worse?

Turning on the fan for the AC or heater. It’s not mold as it is definitely a decomposing animal.

How long has your 2010 Toyota Tacoma had this problem?

Two weeks