I was about to post with this problem too.
I have recently replaced my evaporator and then found there was still r12 leaking.the mechanic said it was from the expansion valve. got it replaced but now the a/c cuts off. when i start in the morning it works fine for about 30 mins but after that the blower just cuts off (with a loud click from behind the central console )and then starts on its own, slowly picks up speed and then cuts of again within 2 mins and this goes on and on but no cooling after that.
I have asked my mechanic to check the belt. there is no slipping and he tells me that the belt tension is auto adjusted in my car.
Can somebody email me the climate control schematics and the troubleshooting pages for the w124 300ce 1989.
It would be a great help in solving my problems with the A/c which just seem to go on endlessly.
The temp here is now 48C and a car with a/c problems makes life miserable.

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300CE 1989 Euro Model.
ML350 2011.