The a/c compressor clutch stops spinning and a/c quits blowing cold after running for a couple of miles.

If it is an older vehicle (>10yr and/or >150k mi) it is very often the air gap on the compressor clutch. On some vehicles this is a 5 minute fix that costs no money as long as you have some basic tools. For safety reasons, I am not going to recommend doing the test as it can be very dangerous. However, if there was some way that the stopped clutch plate could be tapped while stopped and it reengages and starts turning, that is a sure-fire sign of too large of an air gap (it could take a decently strong tap). On my 2006 Sierra all it takes to reduce the gap is to remove one bolt out of the center of the clutch plate (accessible side of the pully). Then after pulling the clutch plate out, inside the center shaft will be a small washer (or a few). You just remove one of the washers (be sure they don't fall out as you remove the clutch plate) and then put it all back together. The air gap will be reduced and your A/C will be working fine again. That being said (VERY IMPORTANT), you need to ensure that after you start the vehicle with the A/C turned off, that the clutch plate is not spinning. It must have a large enough gap to stop rotating when the A/C is turned off or you will burn up your compressor.