Thanks. This explains why there was so much resistance to flow when I was pumping liquid flush and degreasing agents through the evaporator. The tubes are necked down 57% on the 12 mm input liquid line before going through the fin tubes and necked down again 20% as it exits the 14 mm output line. I assume this was done to increase turbulence and dwell time in the evaporator to increase cooling efficiency.

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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