First problem is you have R-12 gauges and R-134 fittings on the car. The car has been converted at some time and will require different gauges, or better yet, be converted back to R-12 freon.

You can find a lot of reading on this site and others about problems when these cars are converted to R-134. My 500 Had been converted but never worked very well. I finally flushed out the 134 and it's oil and replaced the necessary parts and recharged the system with R-12 and never looked back.

Sorry to have to tell you that but it is what it is.

Paul

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84 500 SEL (307,xxx miles)