The compressor Speed sensor MUST match the Tachometer/Engine speed
sensor(s) information.Otherwise the HVAC control unit "C.C.U." will release
the Electrical power to the compressor clutch (Electro/Magnetic).Which is
supposed to "Save" the Serpentine Belt Which ALSO powers the Water Pump
and Radiator Fan.

In His Galactic Majesty's Imperium (Mr. Murphy,of "The LAW")
IT MIGHT be possible [I Guess ???] for both the Compressor Itself AND the
Clutch to go bad simultaneously ?

BUT would a bad compressor Clutch EVER Lock Up ?

I've (In my limited experience) only heard of compressor clutch failure
resulting in Lack of Engagement.

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'84 300SD sold
124.128