Special effort must be used to prevent moisture from entering the A/C system oil. Moisture in the oil is very difficult to remove and will cause a reliability problem with the compressor, especially if a compressor designed to use R-134a refrigerant is left open to the atmosphere for an extended period of time. If the refrigerant oil is contaminated with moisture, it is recommended that the refrigerant oil be drained and replaced with new oil or a new compressor be used.
If the refrigerant system has been open to the atmosphere, it must be evacuated before the system can be filled. Moisture and air mixed with the refrigerant will raise the compressor head pressure above acceptable operating levels. This will reduce the performance of the air conditioner and damage the compressor. Moisture will boil at near room temperature when exposed to vacuum.
When connecting the service equipment coupling to the line fitting, verify that the valve of the coupling is fully closed. This will reduce the amount of effort required to make the connection.
Connect a suitable charging station, refrigerant recovery machine, and a manifold gauge set with a vacuum pump.
Discharge the refrigerant using the refrigerant recovery machine.
Fig. Refrigerant recovery machine hookup