Here is the Story:
1999 ml320 80,000 miles
My wifes truck . a/c cycling off a lot till it stop working. pump still good but tried direct connexion and clutch would not engage .
To make a long story short , bought a rebuilt compressor and a new pressure sensor, since I figure it involve letting the gas out too .
replace them booth and Refill the system (first vacuum the system for moisture and added the lost oil)

Now it should work but nothing so , so I started testing the electrical part to it . the wire going to the pump is good so as the ons going to the pressure sensor , and I did look for voltage going to the sensor all the way ball to the AAM (all activity Module ) witch is the one that sends the power to the pump and to the (ac fans relay) and nothing.

So the way I see it there is no signal from the AC button inside to the AAM. Well this is a 2 component system there is the (ac/heat Switch) known as (S98) wich contains the AC push button , that sends a signal to a control module known as (N19) witch is the one sending signal to the AAM (all activity module)

I do not see voltage on any of the sending wires but not sure if it has to be an exact voltage to test it or if its a ground loop?

I am looking for a way to test the components for they are expensive , and changing booth would be a lot if only one is bad

I did test circuit 15 , witch provides power to booth components

thanks for any help