When it stops getting cold, see if your clutch on the compressor is still kicking on. My bet, is that it's not. If the system is properly charged, it could be the clutch gap needs adjusting, along with other things, of course. Mine did the same thing, and i skeeted some brake parts cleaner on the clutch(to clean grease,dirt, etc from it), then used a pry bar to bend the top of the clutch in a little(you could'nt actually see the difference after i did it though). It fixed it. No problems since. Also, this is not the correct way to adjust the clutch gap , but it worked for me.