I have a 2007 Sonata. At the beginning of this year I had to have the A/C compressor replaced. When the weather started getting warm and I had to turn on the A/C, I noticed a slight "jerking" in the car as long as the A/C was running. Took it back to the shop. He checked the freon and cleaned it up. Still done it. Took it back, had the cabin filter replaced, still does it. When this "jerking" is going on, the air that is blowing gets warm. I've noticed that if I'm driving very slow, 30 MPH or lower, or at a complete stop - it seems to return to really cold air. However, when I start rolling again, the "jerking" and warm air return. As soon as the A/C is turned off, the "jerking" stops, but I'm sweating bullets! I have a very good mechanic, but this has him stumped. This "jerking" feels like the compressor kicking on and off in rapid session. That's the best I can describe it. It has about 145,000 miles on it and other than this issue, runs like a new car. Anyone have any ideas on what I can suggest my mechanic try next?