Air Conditioning System Evacuation
After the recovery process is complete and all available refrigerant has been removed from the system it is ready for evacuation. Whenever an A/C system is severely low on refrigerant or has been opened for repair moisture and air enter the system. This moisture and air are removed from the system by use of a vacuum pump drawing the system into a vacuum.
Moisture in a R-134a system will mix and react with the refrigerant and oil used in the system. Moisture forms a corrosive hydrochloric acid that corrodes lines and clogs screens and other components in the system. It blends with the hygroscopic oils used in today's R-134a systems reducing their ability to lubricate A/C components like the compressor. Note that performing an evacuation will not remove metal shavings from an A/C system.
Once the system is resealed a vacuum pump is used to draw the system to a vacuum of 29.75 or greater. This will reduce the boiling point of any moisture contained within the system. By bringing a closed system into a vacuum the boiling point is greatly reduced and any moisture in the system boils into a vapor and is carried out through the vacuum pump.
If a system has been opened for repair vacuum should be pulled for 30 minutes or more. Check with manufacturers specifications. If a system is left open and exposed to outside air and humidity the pump down time should be increased significantly.
