Here is a little more information:

Static pressure on suction and discharge is around 125#.

Once the compressor engages I get a vacuum on the suction side, but the discharge stays right at 125#. Once car is shut off, the suction slowly (over several minutes) goes back to 125#.

What does this mean? is this just a low freon condition? Why doesn't the discharge pressure go up at all, not even 5 or 10 pounds? Is there blockage somewhere?

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K