The OP has the early climate control system ACC II with the vertical pushbutton control panel. The aux pump doesn't cause a control unit meltdown on that system.

The later system used 81->, ACC III, has that issue.

OP: you say the fuses are fine, do you mean you have checked the little glass inline 2A fuse under the black cover on the driver fenderwell?

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

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