I found something but I am not sure it will help. I had remembered wrong--it was from an official Mercedes publication for the 190D using the Nippondenso compressor. The book states:

Nominal value at approximately 750 rpm (using an AC voltmeter to measure): min. 0.3 V ~

Nominal resistance of sensor: 530 to 650 ohms

It also states (and again for the 190D); "The compressor is activated as soon as an engine speed of greater than 500 rpm is reached. The control unit compares the speeds of the flywheel and compressor 2 seconds after the compressor comes on (to compensate for clutch slippage during cut-in). If there is a difference of more than 30% as the compressor comes on, the speed difference is checked for a period of 200 milliseconds. If the rpm difference equalizes within 200 milliseconds, the compressor remains engaged. If the rpm difference remains (i.e. due to a jammed compressor) the control unit will immediately cut-out the compressor."