If you look at the article in DIY that I wrote about this AC you will see the scope patterns for the three signals you refer. The compressor speed signal is an AC wave with about 1.5-2v amplitute. The engine speed signal is a huge signal by comparison, probably over 20v amplitude AC wave.

This AC engine speed signal is converted into a DC square wave pulse by the idle controller or EGR controller, I don't remember which. All the other devices looking for engine speed will be looking for this square wave DC signal, although I suspect that an AC signal would be interpreted similarly as the controller is only looking for an up down signal when looking at square waves.

Yes, it is getting hot here in N Florida.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician