While doing an engine replacement I unbolted the aircon pump but unfortunately I mistakenly started to undo the bolt just above the 90 in this picture. 

 

Was a bit of a loud noise. I'm assuming I released some aircon gas? Just curious if it was something internal to the compressor or if it's just the aircon coolant.  

Also it seems to be rather noisy when operated now although still ice cold. 

 

Any help would be much appreciated. 

You've probably gassed off a bit of refrigerant. I'd guess the amount left is now bellow the required amount, and therefore running the compressor dry. You might also find it's not as cold/ takes longer to get those cold bursts. You may also have increased fuel consumption as the efficiency has dropped.

My suggestion is don't run it. The pump could overheat and eventually result in you needing to replace it. If it's quite a bit noisier then take it to get regassed.

I'm not a qualified refigeration engineer, but I am trying to get my city and guilds in it so that I can work on any refrigeration system. It's a very hard test though lol.