a/c runs and blows cold air when you first start it then the compressor will run for about 30 seconds the turns off and on

 

This just sounds like a regular AC problem you would have in any car. your best bet is to get a professional to look at it, because if it's a bad compressor you can't replace it yourself, if there is not enough gas then you shouldn't replace it yourself. you can only pump up the gas a little bit by yourself if that's the problem, but you have to be sure your problem is a bit of low 134a pressure.

 

just had to have the compressor in our 05 330 replaced- AC light was flashing, occasional 'check ac' message, and rattle that sounded like it was coming from right front during acceleration. mechanic said the compressor shaft had broken. replaced it and everything was good again.