95 air conditiner problem

I replaced my daughters ac unit last year and it worked fine all season and now is blowing hot air, I figured it was just a leak so I got a can of gas and the pressure was way high so I didnt add any. a friend of mine said it was most likely one of the switches under the hood, but of course I dont know of what switches he could b talking about. He is in a diffrent state and owns a shop..... does anybody know without me having to buy every control switch under the hood? my haynes manual is no help on this