the a/c amp located behind the glove box. check to see if it is burnt. get a used one from junk yard.
this routine revived my a/c in my w123 after years of non-function.

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD