A/C Problem - Bad Expansion Valve??

[bbrewer]

I've got an a/c problem with my 1991 300SL, and have been working the issue on the Tech Help board, but may need R129-specific help.

Here is the link to the current thread:
http://www.peachparts.com/shopforum/tech-help/127427-c-pressures-equal-causes-post933448.html#post933448

I'm:
A) trying to make sure A/C expansion valve is located where I "think" it is - next to the drvr's side shock mount, and
B) trying to figure out what expansion valve I need.
The system had been converted to R-134 a few years ago, and just don't know if expansion valves are routinely switched out for something bigger/small than the standard OEM expansion valve (or generally left alone) on these kinds of change-overs.

Any experience/thoughts would be greatly appreciated....

Thanks.