The condensor relies on the aux. fan for cooling at low vehicle speeds. Make sure your condensor is clean and your aux. fan kicks in at the appropriate P/T point (~52* with the red switch on receiver/dryer). If you have access to ref. gauages post the high and low side pressures at 1500rpm. and we might be able to tell more. Mercedes has a reputation in A/C circles for being "condensor challenged", but it shouldn't be "unbearable". R-12 or R-134a

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)