You might be a touch overcharged. Rule of thumb for an R-134a conversion is 80% of the R-12 charge. You are a bit closer to 90%.

I ran R-134a for a while in my 124 diesel wagon after rebuilding the a/c system. (I replaced everything but the metal lines.) Was pleasantly surprised at how well it cooled, despite all the bad stories. I'm trying to recall how much refrigerant I used - think it was 2.5 cans - maybe 30 ounces?

MB says to check the high side by running the engine at 2000RPM for 10 minutes, fan speed on high, car in the shade. This will produce a higher number than you are seeing at idle. I don't have the shop manual handy, but if this test produces a number above 300PSI you are likely overcharged.

On the other hand, if the pressures are under control and it cools OK, then by definition it's charged right.

- JimY