After bypassing that pressure switch, verify the PBU works. Ground pin No 10 to the battery, should have 0 (zero) ohms when the PBU is set to an A/C function.

If both check out, jump the compressor. Pins 5 and 7. That will get it to stay on...

The speed sensor could be bad. The Klima relay too.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
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Six others from BMW, GM, and Ford.

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