No, it is very unlikely to be a control unit problem.

The most common problem is the blade type fuse on the left fender ahead of the standard box. This is a special fuse and the current flow causes them to expand and contract till they crack from fatigue. That simple problem is probably most common, look carefully as it is often not obvious.

The next likely problem is the blower itself or the regulator below it under the windshield wiper assembly. There is good description in the archives on simple electrical testing at the three wire connector by the brake booster the verify whther the problem is in the blower are or in the control circuit.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician