If you pull it the whole HVAC apart, you'll see a large Siemens casted on the top of the evaporator case.

If you are not pulling it apart, it is harder for the untrained eye by looking at the shape of the box. But you can also tell by pulling and checking the blower, if it's original to the car. The Behr blower will have a caged center on the fan. The Siemens blower fan is solid in the middle.

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1983 123.133 California
- GreaseCar Veg System

So you can't tell unless the blower is the original to the box? If I post a pic of the underside of the box that's in the car, can you tell which box I have?

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked