The Stovebolt Site Forums The Shop Area The HiPo Shop A/C question

There should be no reason to replace the oil if the system had no mechanical failure. If you are going to purge with nitrogen to help expel refrigerant/atmospheric contaminants, you would do that prior to the evacuation. Be careful with the nitrogen, tank pressure is extremely high, you need a regulator on the tank and you don't want to pressurize the ac system beyond its high side pressure rating. Also, don't blow the oil out of the system if you don't plan on a total oil replacement, you will have no idea how much oil is left in there. You don't want to "overfill" with oil because it takes up volume that should be refrigerant.