Truck Repair: air conditioning intake, ford f 350, ozium

Question
I have a '99 Ford F-350 CC Lariat with a 7.3 PSD.
Recently, when i turn on  the A/C, the first few moments it blows musty air. I would like to introduce  Febreeze or Ozium into the intake filter, but I do not know where to look for it. Can you help me find the intake?

Thank you, David

Answer
well you should look on the pass. side floor board should be a flat air intake there. also make sure that the water is draining out under the car.after running the car for about 10 min. there should be a puddle under the truck just befor the pass. side door .that smell might be the sign of something thatneeds more attn. on the intake if there is any question put a piece of paper in front of it and it should suck it in while running.thanks for the question. if you need anymore help just ask