Ok, so I testing the low pressure port and it reads 95psi, the temperature outside was 60F. This was with the A/C on full with the engine at idle, the compressor did not engage though.

I don't know where the high pressure port is so I didn't test it; I think it might be on the dryer? I then waiting for about 2 hours to let the engine cool and tested the low pressure port again with the engine off and it still read 95psi.

Tomorrow I plan on checking the fuses and relays and jumping both the AUX fans and compressor sensors on the dryer to make sure that they're all working.

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500