Crankcase pressure and electrical load

[meerkatmag]

I fitted a madman computer and a bunch of sensors to my 2.5 di turbo. One of the sensors is a crankcase pressure sensor.

I'm seeing some odd behaviour and wanted to know if anyone has any explanation for it.

Basically under normal driving it has 0psi of crankcase pressure, this is under all conditions, cruise, acceleration idle.

However if I pull any electrical load, like putting the heating fan on, headlights or wipers then the crankcase pressure goes up. This happens at cruise or idle.

With everything powered on the pressure reading is only around 1psi so it's still very low but i just don't understand why this would happen.

Other engine loads, like driving up a hill doesn't increase crankcase pressure at all, so why would alternator load?

Anyone have any thoughts?