its a 1990 gmc truck?

?? What & how do i check on why my air conditioner is not blowing out cool air? I think I"ve had this problem for the last 2 or 3 yrs. I"ve owned my truck for 21 yrs I love my truck,(I am a 55 year old Female who owns & loves her truck for 21 yrs.)I dont drive my truck every day let alone drive more than 8 miles in a given mo. Air was not top priority. Yes my baby needs some well deserving tlc applied under her hood, this is one reason why we dont drive often or venture to far from home. Shes not nickle & dimeing me, if I have enough gas to get me to the store & back. 80 to 90% of the time if I need to go she doesnt let me down! As far as my air cond. Does it need to be recharged, is it leaking maybe Im lost please help me out if you can. Thank you for my long winded ??????? 1990 GMC 1500 sierra 350 8cyl. TBI 150,ooomi. enough info?