I recall that at 70 or so outside you should get something in the range of 90 lbs of pressure with the system standing still. Refrigerant expands greatly with heat, however, so at 90 ambient I wouldn't have a clue as to what you could expect--one fifty might not be unrealistic with the higher-running R-134a.

I have a sneaking feeling that there was some of the old R-12 still in the system. It can hide in the oil and leach out over time. When R-12 and R-134a are combined they make an azeotropic--I may have the spelling wrong--gas, i.e. one whose pressure when heated runs higher than either of the combinants. My recommendation is to evacuate the system and be sure it is held at a vacuum for an hour or so after you have it as low as the vacuum pump will take it. That should remove all of the old refrigerant and any moisture present. Then add some oil and recharge with two cans of R-134a.

Good luck.

-Steve