A/C compressor replacement W210

[graysilm]

I just had the a/c compressor replaced in my 1999 E300TD. I posted in the diesel discussion and didn't get a response so that is why I am posting here. My old a/c compressor clutch was making a loud noise and I was replacing a lot of my belt components so I decided to replace the compressor at the same time. My old compressor was still engaging (slowly and loudly) and was blowing cold air. The mechanic who installed my new compressor called me today and said that he after he pulled a vacuum on the new system he then charged it to the correct pressure before turning the key on and turning on the a/c button so he could complete the initial charge to the correct pressure. He said that new new compressor will not engage. I have heard of some weird electrical glitch that can cause this. Does anyone have any idea what may have gone wrong, and what can be done to fix it? Thank you in advance for any advice.