Got NO A/C and lucky me it's only been in the 90's with 90% humidity

My next door neighbor is an Army mechanic and is the captain of his squad. He is telling me to take the car to Wal-Mart or K-Mart and have them re-charge the A/C....

I know he's good at what he does, but may I have a few more opinions or is this an easy enough DYI?

Thanks