There is a little bit of Black Magic in charging an R12 system that has been converted to 134. To begin with, you should only charge with about 80% of the original R12 volume. Secondly, there is a point where if you add just a little more R134, the high side pressure will "run away." You do NOT want to hit this point.

If there IS a restriction, I don't think the expansion valve would be suspect. If it WERE the culprit, it is your restriction device in the first place and the low side would get lower and the high side higher, not both sides getting higher.

Good luck Doctor Eric,