Before getting carried away, make sure the electrical portion of your system is working properly. You shouldn't have to rev the engine for the compressor to kick on. Since you have a 1985 model, you could have Klima relay problems or issues with the Tach signal.

When you did the work, you DID pump the system down into a deep vacuum to boil off any moisture right? If not, you will need to do so or the system will never work properly.

R134A is far less efficient at heat transfer than R12. The A/C system in the W123 was marginal when new and will be less than spectacular with a conversion. Charge by weight and use 80% of what the system calls for in R12.

Make sure you installed PAG or POE oil in your system. Mineral oil is not compatible with R134A.

Additionally, airflow is your friend. Take degreaser and clean out your condenser and radiator and blast it out with a good hose (don't bend the fins!!!). Make sure your engine driven fan is in good working condition. If the clutch isn't engaging when hot, you're losing a huge amount of airflow through the condenser.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)