This is a common problem. The most recent I have seen was posted by someone else on this board after I replaced my CCU. On mine, the new CCU did fix the problem. The other post indicated that a worn key switch could be causing the problem. Try jiggling the key when the blower cuts out to see if that has any effect.

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1984 300SD 326,997 miles and counting . . . No wait, my odometer is still dead