1989 F250 AC Question

[George1]

Good morning. While driving the truck this morning a loud intermittant screech started coming from under the hood. The noise then became steady, very loud. Stopped, kept the engine running, checked a few things then saw a cannister labeled Climatizer and Air Conditioner. Whacked it with palm of my hand, and lo and behold, the noise stopped. AC still works. Is this a sign of impending doom of my AC? Not finding any info on what this thing does. I expect that if I replace the can, I will have to degas the system so I would like to avoid that. I can live with whacking the thing once in awhile as the truck gets only a few hundred miles a year put on it.

Thanks for any responses.