when i turned the a/c on and looked under the hood a loud burst of freon came out the back of the compressor is it the compressor all together?

 

When mine went it blew out the front. If there is a knocking Id replace it. I have a 1999 durango and only cost 140 for a new compressor. Pretty easy to do too. Dont forget to change out the evap canister too. Whole process too about hour and a half. Make sure you have a manual of some sort though.