About 2 months ago, the AC went out on my wife's 2004 Grand Cherokee. It just wouldn't blow cold air, I tried to charge but it would never charge so we just didn't use the AC. However last week she was driving it and all of a sudden she started getting this really loud noise from under the hood almost sounding like it was going to blow up. I drove over to meet her to see what was going on as I told her to park it. I noticed that the vehicle drives normally and when I cut the AC off, the noise goes away. Anyone know where I can start with respect to troubleshooting this issue? The serpentine belt seems to be doing fine. I can post a video of the noise if it would help.

 

Sounds like it's probably the ac compressor. With the hood open & the engine idling, have someone turn the ac on while you watch/listen to the compressor. See what happens when the clutch on the front of the compressor starts to spin, or if it locks up. If there's a problem, either you should replace the compressor, or have a new clutch installed on that compressor, as the compressor comes on whenever the defrost is used also. You might want to take it to an ac repair shop for an inspection if you need further info, or can't fix it yourself.