Just had two different techs look at the A/C on our1987 300 SE(euro).
When highway driving the car takes it's time but does get nice and cool(just cool and pleasant - not cold). In the city stop & go traffic which we do a lot of - forget about it. It really doesn't cut it.

The first tech looked at the sight glass, poked around and said that all the car needed was more R-134 .
The second guy was more thorough but less conclusive. He checked the system under pressure and did not think it was lacking gas. He said the mono valve is good, the main flap does close,the pressure switches seem fine - the fan works(even though it does not come on automatically when the air is on ) The engine runs comfortably just above the 80C mark and the A/C does not seem to put a big strain on it in terms of heating up.
But it does not get very cold. As a matter of fact, when the RPM's drop as we shift into gear from park - the temp. rose on his digital gauge by a few degrees C.He was not sure about that. The one thing he did suggest was changing the green system(pressure switch..) to a red one - that get's the Fan going earlier than 107C, thus helping the A/C in warm climates. Anyone try that before ? or know about It?

a seperate question - the vent for the back seat passangers will only blow hot air-all the time, no matter what. Is that a vacuum problem? how can one track it ?

Gotta love this forum..