Ran across a strange situation the other day,
but with cars....that's normal. The AC compressor was replaced two months ago from a w/d supplier on a 86 300E along with a new
expansion valve, drier and pressure switch(red) of course. Everything worked fine for two months and then quit working. Upon checking out the normal found the rpm sensor to be at 226 ohms vs. MB manual of 590+/- 60 ohms. Pulled the sensor out but it was about 3/8" longer than an OE and the seal was around the larger diameter under the snap ring. An OE has the seal on the small diameter. Checked supplier and found all the sensors ohm at around 225-228 and compared compressors. The rear boss is about 3/8" higher than an OE! Put the original sensor back in and replaced the klima relay to fix the problem. All working fine now.
The crux is, there are aftermarket compressors out there because of the demand
for a less expensive replacement but if you need an rpm sensor, forget an oe, as it won't fit. The clutch, who knows. The compressor looks exactly like an oe and bolts right up. Of course the Nipp label is not there. Be carefull techs!!
300SE, 300CE, 190/5.0