Lee,

Doesn't seem like the expansion valve is throtaling the freon correctly. Do a search on the Larrybible. He's one of the better A/C guys on the list.

How much freon have you added. It was completely empty before- I believe that system is right about 1 kg or 2.2 lbs.

If you are looking for a leak in the evaporator, I think many ppl add a florecent dye and check the condenstation water with a black light(that's my plan).

If the shrader valve is your leak point, they can be replaced with out discharging the system with a special tool. I purchased mine in 2000, and it was about $30-35. A appliance store ordered one for an R-12 system. Low side is always easy-high side valve I'm not sure if there is enough room to get at it. Was a bit tight- but I managed to do it on my W123. My W124 has both of them leaking.
Previous shop said they couldn't find a leakage... I'm going to assume his gauges were still connected. He was a very well respected Mercedes tech and checked the evaporator.
If the system was not completely empty- I wouldn't worry about a dryer.

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E