[MARKDTN]

I have always used compressed air. If you have a dryer on your compressor and pull a good vacuum you should not leave any moisture when you are done. I just put 100 psi into both sides, close the valves, and let it sit 20-30 minutes. If the needles stay put I let it out (slowly so you don't loose any oil) and pull a vacuum for 45 minutes or so and I have never had any issues. If you have access to nitrogen I'm sure that would be even better, but a good longer-than-usual vacuum should get all the moisture. A compromise might be to pressurize with shop air with an old dryer to check for leaks and change it before the vacuum and charge since the dryer media is where moisture can be captured. Then you only have 2 fittings to worry about. Won't help with your situation, but may help someone with a stock system.