air conditioning....yes or no?

I draw a vaccum by connecting to manifold pressure to get most out, isolate w/ valve, then use a Mighty-Mite hand pump to get way down. Takes ~2 min of pumping. I let it sit 30 min and re-pump. Pressure goes up slightly due to outgassing and water evaporating, which is the main reason to pull a vaccum.

If you don't know what it had, and hate dealing with shops like me, you can add an HC refrigerant. Many brands, I have used Duracool. It mixes with R-134A or freon and all oils, and works even better than freon. Some will scream "flammable", but R-134A is flammable and poisonous, plus being outlawed by EPA. Soon new cars may use HC.