Check the wiring to the inside temp sensor. I don't know if it's in the center of the dash like the 123 (access through glove compartment) or in the overhead with the dome light like the 124. If one of the wires is broken, the CCU won't work correctly.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970