190D 2.5 (201.126) L5-2.5L DSL (602.911) (1987)
Engine Speed Sensor: Description and Operation
Engine RPM Sensor
PURPOSE
The engine RPM sensor which is located at the rear of the engine, senses flywheel rotation.
CONSTRUCTION
The RPM sensor consist of a magnetic core and a coil (monolithic sensor).
OPERATION
When the A/C system is engaged, flywheel rotation causes an alternating voltage to be induced in the coils of the RPM sensor. The frequency produced
by the alternating voltage informs the compressor cut-out control unit of the engine speed. If the engine speed differs more than 30% from that of
compressor speed, the compressor cut-out control unit considers the compressor to be jammed (overcharged or internally damaged parts) and disengages
current to the electro-magnetic clutch in order to protect the common engine drive belt and accessories.