I have the exact same problem. I have a 2002 Chevy Silverado 1500 series and at idle It overheats and the air conditioner stops working. I have previously had it charged and that only helped for about a month. I also replaced the fan clutch. To no avail. You can hear the compressor kicking off the makes a loud thump. The vehicle only cools down when bringing the RPMs up to 2,000 and the air conditioner works fine at that point. I noticed the new fan clutch is working and it seems to be spending when it's overheating. One more important thing that I noticed today was I didn't even have to have it at a higher RPM the temperature went down when I was coasting down the hill for 2 miles and started blowing really cold air