Fyi: I know starting in the 1983 model year, there are two original manufacturers of the evaporator box . Siemens and Behr. The evaporator itself do not interchange between the two brands.
Before you order an evaporator, make sure you check to see which manufacturer you have. I made that mistake, ordered a brand new evaporator for a Behr box and it didn't fit my Siemens box. I ended up getting a whole box out of the wrecking yard and another evap from a forum member. I used wrecking yard one and kept the forum member one as a spare.
Btw- the Siemens evaporator core is about a 1/2 to 1 inch wider that the Behr core.

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1983 123.133 California
- GreaseCar Veg System

Great information! Do you know where to look for a brand marking on the evaporator box by chance?

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'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild

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