99 Dakota 5.2 V8...I can hear a really fast knocking when my compressor engages...sounds like a woodpecker...I added 134A and still have same result...Sometime cold air comes out, but usually not very cold...Bad compressor, or Air in line? Help!

 

sounds like your fan, my BMW did it once, the fan it self came off the roller an whenever i would turn the fan on it would slide forward an knock against the casting, usually u cant fix it with out replacing your fan, but u might be lucky an pull it out an put a C clip on the end of the rod that the fan spins on, not sure how hard it would be to replace the fan cause i havent had to do it on the durango yet but as far as i know it should be under the passengerside dash coverd up with a black plastic sheild..