[wwest]

When you "hang" the r-134a adapters on the manifold for storage are you certain you have fully "unscrewed" the adapter plunger that depresses the Schrader pin?

One other point. It is my understanding that the release "stem" on some Schrader valves are long enough that they can be damaged, bent, if you screw the adapter's Schrader pin plunger in to far.