[Are you using the (do you have?) FSM ?]

The Klima compares the speed of the Compressor to the speed of the Flywheel
and if they're out of It's "specs" ,No clutch engagement.

If your Idle is @ 600 RPMs ,Does not the '87 still have the "Turn and Click"
Idle speed adjustment Knob?(So, that you can turn the Idle up to 750 RPMs)

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'84 300SD sold
124.128