[TrekGTO]

Originally Posted by GT-ER

http://sanden.com/pistoncompressors.html
I've actually disassembled these before. The only electronic component is the pressure valve and sometime they fail.

Pulse width modulation is the internal clutch, which is how they have 0 output with no external clutch. Having done VW service for 35yrs this function is the leading cause for replacement. Car comes in with 0 compressor function at any rpm. I have yet to see a compressor with no clutch function but I am 2 yrs behind. SS Sedan has pulse width modulation and an external clutch.