strange ac problem
 

I was driving home today doing 70 and I noticed my ac was not as cold as before but it was still cool so I didn't think anything of it. A few minutes later I thought I saw smoke come out of the vent but no one else saw anything so I turned the blower off completely, waited about 2 minutes then turned it back on. it was fine after that for a few minutes then gradually became warmer. I turned it off again but it stayed warm. I have never experienced a problem like this before, the ac has worked fine up until now and I don't know if I should try to recharge it or just take it to a shop? The vehicle is a 99 s80 t6. Any help would be greatly appreciated thanks.