R-1234YF Refrigerant System Evacuate: Notes
If the A/C refrigerant system has been open to the atmosphere, it must be evacuated before the A/C system can be recharged with R-1234yf refrigerant.
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 A/C compressor.
Moisture and air in the A/C refrigerant system will raise the compressor head pressure above acceptable operating levels. This will reduce the performance of the A/C system and damage the A/C compressor. Moisture will boil at near room temperature when exposed to vacuum. Always use an R-1234yf refrigerant recovery/recycling/charging station with a vacuum pump that meets SAE standard J2843, or an R-1234yf compatible manifold gauge set and a stand alone vacuum pump.
If an A/C compressor is left open to the atmosphere for an extended period of time, it is recommended that the refrigerant oil in the compressor be drained and replaced with new refrigerant oil to reduce the possibility of contaminating the refrigerant system. Refer to OIL, REFRIGERANT, STANDARD PROCEDURE .