Brother of The Benz
Steve, you really got the gray matter whirling.
As I remember pressures and temperatures, water boils at 33*F at 1 micron Torr. Help me out if these figures are in error. I think you get the drift of it!
For our auto applications R-12 boils at 32*F at 30psig evaporator pressure.
With these figures we can see what occurs at the expansion valve should there be water, ever so small an amount, it will freeze and restrict the flow of refrigarant. This can be seen on the low pressure gauge, blank-off from the compressor.
After having your system emptied by a certified Freon re-cycler, evacuate the system as long as you have time. You can never overdo it.
Burr my R134A with the addition of a "Hot Shot" charge does fine.
Happy Trails Beep Beep from The Spiderman in Houston!!!