I seem to have a weird musty smell when starting after it has set for hour or two from running ac at max What could be the problem 97 F150 5.4 converted from 4.6

 

My 03' had a 'cat pee' smell when I first started the A/C, so I bought some A/C deoderizer from AZone for about 8 bucks. I sprayed it through the fresh air vent thats below the windshield wiper blade on the passenger side while the A/C is running on MAX. Also sprayed the inside vents with A/C off. It has worked good and the smell from the deoderizer wasn't bad. The name of the product is: A/C & Heater Duct Cleaner. Go to www.efproducts.com for more info.

 

But if you can disassemble and clean the ducts first that would be better.

 

Ford had a problem with a slimy, smelly fungus growing on the evaporator cores from that era. I had to change a few myself, but Ford says they can be cleaned. See if you can find a TSB about it.

 

My owner's manual says not to park the vehicle with the system set to MAX. Switch it to VENT before shutting down.

 

Thanks for the replies looks like I need to do some cleaning

 

Good luck getting rid of the smell. Years ago our cat hurled in the cowl vent on Dad's 66 Mustang. Man, he 'bout never got the smell out! It was in the winter and we preferred to freeze rather than smell heated cat puke!