hi i just bought my first hyundai an 02 sonata lx - she's beautiful but, i have a problem with my a/c it blows cold for about 15-20 min. then it blows warm for about 15 min then back cold. sometimes it gets stuck on the warm cycle for about 30 min. i thought it needed freon so i took it in and had a/c check done they said they added almost 1lb. i still have the problem any ideas?????? thank you in advance for your response