As I look at the white intermediary tubes, it appears they are flattened somewhat, is that correct? If so wouldn't that increase the backpressure regardless if the condenser is parallel or series flow?
Not having these adaptor pipes is the only thing that has prevented me from converting my 300TD to parallel flow (and from R134A back to R12! )

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body. '87 300D w/ Sportline suspension. No more '79 300TD w/ 617.952 engine at 367,750, it was my annual driver to Texas and I sure don't miss it poor A/C heater system!