I have a 1999 E300 turbo diesel. Compressor had been leaking refrigerant for 3 months. I installed new Denso compressor w/ clutch & receiver dryer & expansion valve at the same time. The clutch will not engage. Ran a scanner test and got a code for coolant temp sensor, replaced that & still no power other than 7volt at the compressor. I have read that the current to compressor clutch comes directly from the control head in the dash, and
reset and cleared codes also
Where should I check next?

There is a pressure switch which keeps the compressor from running if the refrigerant is too low or too high.

With that said, you don't mention what your refrigerant pressure is????