My ac is blowing hot air I refilled with r 12 an still can get cold

Hi. First of if your using R12 then you've started on the wrong foot. Your truck likely uses R134a. Really the question is, is there anything in the system? If its already full and doesn't work then we'd ask, is the compressor running? If it is not running, then why not. If yes, then what are the pressure reading on high and low sides. Also there should be a label under the hood that tells you how much R134a the system takes. If was totally empty and it takes 2.25 lbs and you only put in a pound then it would still blow warm. A professional tech should be able to sort this out for you in no time.