I'm not sure if the compressor actually turns on. I'll look into this.

I'm planning on taking a look at the blower motor brushes, but could worn brushes be a cause if the CCU and blower works when it's heating, but not when it's hot outside and the temperature dial is set to blue/cold?

I believe the ambient sensor is on my dashboard. It seems that when it's hot out and the sun is directly on the sensor while the car is parked, is when the blower won't turn on, unless the left CCU button is engaged.

The blower will turn on when the fan is set to high, but turns off after 20-30 seconds.

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1985 300D Turbo Diesel W123 Federal