Did I understand correctly when you said you "valved off the high side" I took it you mean you closed the liquid line and pumped the unit down? If so you won't read any pressure because your high side gauge is reading on the side opposite where the refrigerant is accumulating, and the low side won't read either because its getting pumped into the condenser away from your low side gauge.
While its pumped down like that I'd put a small amount of refrigerant into the low side and put a lot of nitrogen pressure in with it and go over it again. (maybe as high as 300 psig) Also look for signs of oil on the outside unit.