Perhaps you have a blockage but I would think that your low side would go into a vacuum state if the expansion were truly blocked. High side would go up but if the refrigerant was blocked then there is little, or not getting past the blockage. Maybe some other times need to be examined prior to jumping into an expansion valve replacement.

Have you checked?
Mono-valve (split rubber seal on insert)
Mon-valve (electrical control, grounded through pushbuttons)
A/C comp (Always on, regardless OR with A/C demand)
ETR (quite possible IF A/C demand-comp runs continuous)

Let's explore some of these other contributing factors to determine if there is pressure issue to address.

BTW: Was the A/C system converted to R-134?