The little elbows off the vacuum tree have become a leak point on my new to me 300E. PN - 201 805 01 03. I recently replaced all of the pods and did about 42°F from center vents on 134A down the freeway with the fan on low speed. I am just running 134A for now until I replace the entire system. Probably will dump it and slip in 152A as the pressure curve is nearly the same as R12. SAE has a really interesting research paper on it. Worth the read.
My city creeps up more as the fan clutch is dead (last check was about 59°F at idle when it was just under 100°F), so the aux fan is wired for low speed always currently. I swapped in a 16" Spal (barely fit, I mean really tight) and since my tensioner is dead it loaded my alternator down too much causing big time belt slip. M104 mechanical tensioner time for me.
30102049 is the part of the Spal I wedged in there. Just this on high speed moves a pile of air. I plan to use it on low speed with A/C and my 91°C trigger (with a resistor) in conjunction with the aux fan as normal AC pressure driven. Then use high speed at 99°C. Zip me a PM with your email and I will send a few photos of the fan mounted.
Rock Auto has a listing for a parallel flow condenser for the 300E from about 1991 on. The AC hoses are slightly different, so you can buy a set from a later car or just modify yours accordingly. I feel this is the only way you will receive adequate performance from 134A in the 300E. Honestly, I would do it even with an R12 system.
I do notice if the car has sat in the sun for an extended time, it will take a LONG time to cool back off. Utilize one of those windshield reflectors and park toward the sun to reflect what you can. Drive with the windows down for a bit when you first get the car going. It is easier to cool 100°F air than 150°F air.
I am in Texas so you know.