Siemens Freezer alarm keeps sounding?

I have recently had the Compressor break on my Freezer and I had to have a new one fitted by a freezer engineer (the insurance wouldn't cover the price of fitting a new compressor) so I got an independent repairer to fit the new one. Well my question is. when re gassing the system was the engineer supposed to evacuated the system before installing the fresh aircon gas?
The reason I ask is since the job has been done, whenever we refill the freezer with fresh food after a (big) shop. The freezer isn't completely empty by the way. the alarm buzzer goes off telling me that the temp has dropped down. and it stays like that for at least 12-24 hours. I am sure that it shouldn't be doing this as it never did before I had the compressor fitted. The reason I mentioned evacuating the system is because I am an licensed aircon engineer for motor vehicles and whenever we fitted any new component on the aircon system I would have to pull a deep vacuum on the system to make sure there was no impurity in with R134
Gas.
I do hope I haven't complicated my question too much please ask me clarify if needed.
As I have already said this (problem) wasn't there before the new Compressor was fitted. We had the Freezer for five years, and up until then and we never had the alarm come on when We restocked even with a (big shop). I understand the need for the Freezer to have to get back up to (or down to) the correct temp
Hope this additional info helps.
All I really want to know is should a deep vacuum be pulled on the A/C system before installing the new A/C gas?