1998 Jeep Cherokee: The air conditioner compressor sometimes makes a lot of noise (like its about to fall apart) when the control knob in in the “on” position. Since its intermittent, I was wondering if it is more likely that the bearings are going bad or is the compressor failing - or other ideas. If it is the bearings, can they be replaced without replacing the whole compressor or is that not worth it?
Compressors run intermittent; they cycle on and off. If it sounds bad, it probably is bad; rough and noisy running is usually a sign that it’s on its last legs.
As Docnick said the AC compressor runs intermittantly. There is a bearing in the clutch assembly that allows the compressor pully to idle freely when the compressor is not turning. This usually makes noise continuously when it has gone bad. Only this bearing and idler bearings can be replaced without letting the system down, i.e recovering the refrigerant.
If you want to trouble shoot this noise a little more, run the AC; watch the front of the compressor pully; and notice when the clutch plate starts spinning. If the noise starts when that clutch plate starts turning, the compressor is failing. Compressors can be rebuilt locally but the tools and cleanliness required mean that the job is best done at a dedicated, quality shop. Once a compressor starts making noise, enough debris has been made that the whole compressor should be disassembled, cleaned, worn parts replaced, refilled with the correct oil, and the unit resealed.