Whenever a repair to the AC has been done, or a leak has been fixed, you'll need to recharge the system with refrigerant. This involves hooking up your vehicle to a machine that will remove all the gases with a vacuum pump. They will hold a vacuum for up to 30 minutes to insure you have no leaks and then recharge the system with the refrigerant specific to your vehicle. Most vehicles made before 1995 use R12 which is more expensive than the r134a found in newer vehicles.