Another possibilty is a defective A/C pressure switch. This should turn on the electric fan in front of the condensor when the refrigerant pressure exceeds a certain amount. The air across the condensor cools both the refrigerant and the radiator. If its defective, you will run hot at idle. A sepearate function causes the same fan to come on when the coolant reaches a particular temperature - 105 C sticks out in my mind, but I'm not certain and don't have time to check right now. Do a search on these for more info.

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Tjohn

82 300 SD
77 450 SL (gone)