Is It:
Low Refrigerant
or
Bad Switch
?

If you've NOT enough Refrigerant, even with a good Low Pressure Switch
You'll not get any Joy.
(And you don't wanna FORCE the compressor to run on LOW Freon,for very long)

'Got a set of gauges? (To check for Refrigerant)

If you jumper the wires that connect to the Low Pressure Switch on the R/D
Does the Compressor engage?

If you've got Freon and the Comp doesn't engage/BUT the comp engages
when you jumper the LPS wires ,It's the LPS that needs renewing.

The Open Circuit on the LPS is just telling you there's not enough pressure.
(Or you have pressure and the LPS has traveled South.)

Klima relay HAS been known to screw with more than one MB owner.

1. Check for proper freon level/pressure, correct as necessary.
2. Try "Jumpering" the LPS.
3. Then look askance @ the Klima.

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'84 300SD sold
124.128