If the refrigerant system has been open to the atmosphere, it must be evacuated before the system can be charged. If moisture and air enters the system and becomes mixed with the refrigerant, the compressor head pressure will rise above acceptable operating levels. This will reduce the performance of the air conditioner and damage the compressor. Evacuating the refrigerant system will remove the air and boil the moisture out of the system at near room temperature. To evacuate the refrigerant system, use the following procedure:
- Connect a R-134a refrigerant recovery/recycling/charging station that meets SAE Standard J2210 and a manifold gauge set to the refrigerant system of the vehicle.
- Open the low and high side valves and start the charging station vacuum pump. When the suction gauge reads 26 inches Hg. (88 kPa) vacuum or greater, close all of the valves and turn off the vacuum pump.
- If the refrigerant system fails to reach the specified vacuum, the system has a leak that must be corrected.
- If the refrigerant system maintains the specified vacuum for five minutes, restart the vacuum pump, open the suction and discharge valves and evacuate the system for an additional ten minutes.
- Close all of the valves, and turn off the charging station vacuum pump.
- The refrigerant system is now ready to be charged with R-134a refrigerant.