A/C problems

I recently retrofitted the A/C to 134A on a 92 300E. I replaced the compressor, drier and the expansion valve. The problem is that the a/c isn't cooling like it should (50 degrees F ). Guage pressures are at 40 and 250 and outside temp is in the mid 90's.
I noticed that the expansion valve is the same part number as the old R12 exp. valve. Is there another exp. valve specifically for 134A? If so, could this cause my cooling problem? Thanks in advance for any help.

Larry...