The compressors can have problems with the electrical devices that turn the clutch on. A lot of times you'll hear the clutch kick on when the air conditioning clicks on and off. There are pressure switches throughout the system. There is a low pressure cutoff and a high pressure cutoff and on most late model vehicles, they are controlled by the computer that controls everything in the car. It will look at those sensors and the computer will determine whether to turn the air conditioner clutch on and off. Another problem is there is a sealed unit in the front that you cannot see that can leak. There is a big O ring around it that can leak and there is a seal there and then there are two seals on top where the line assembly that goes on. There are a lot of different points where leaks can occur that would require removing and repairing or replacing.