Depends on what's causing the problem. If the belt is getting chewed up, that is the result of a misaligned pulley. That could be the AC compressor clutch pulley. Those can usually be replaced separately but on many cars there isn't room to get the puller in there so the compressor has to be removed and be repaired on the workbench. That job is rather labor-intensive and you still have the old compressor when the job is done. Since AC compressors are a common failure item, most conscientious mechanics will elect to replace the entire unit if they have your best interest at heart. The overall labor will be lower but the parts cost will be higher. Also, the chance of doing something incorrectly is reduced.
Regardless if the compressor is replaced or it just gets a new clutch / pulley, when it has to be removed, the refrigerant must be recovered first. That requires a very expensive machine. Most of them also clean and recycle the refrigerant so it can be reused later. It is always recommended to replace the "receiver / drier" whenever the system is opened for any service. Humidity from the air will get into the system where it can cause corrosion and interfere with proper system operation. Water and refrigerant combine to form an acid that will eat metal parts. If water circulates with the refrigerant, it will freeze and block the flow at the tiny port where the pressurized refrigerant expands and gets real cold. You'd experience the same intermittent loss of cold air as if the AC compressor stopped running.
The receiver / drier has a desiccant in it that can absorb about ten droplets of water. It also has a filter to trap tiny particles that flake off rubber hoses or corrode off metal parts. As that filter becomes plugged, it becomes the point at which the pressure changes and the refrigerant becomes very cold. The cooling would take place under the hood instead of inside the car.
Some mechanics do not replace the receiver / drier in a misguided attempt to save you money. If they're lucky, they'll get away with that, but eventually it's going to come back and bite them in the butt. Then they'll be doing the job over and they'll have to charge you for the additional part. For the reliability of the repair, experienced mechanics will replace the receiver / drier without question.
They will also pump the system into a very hard vacuum for half an hour. In a vacuum, water boils at 77 degrees F. And turns to a vapor which can be drawn out, THEN they inject the proper amount of refrigerant. The final step is checking for leaks with an electronic tool, and verifying proper system performance.
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Monday, October 21st, 2013 AT 2:58 PM