I think you are referring to the compressor. On my rig it's under the drivers side just behind the condenser which has a 12v fan on it. This fills with debris on a regular basis and jams up.
If you don't have a Starcool III manual, search on this site. I think there are downloadable copies. I had my compressor box open a year or so ago. I don't recall the parts inside. Sportsmobile might be able to help but they kind of run from these things now. Dark and buggy here now, not going under.
To learn anything about the system I typed "Starcool" into the search function and read every thing but the member classifieds. Good luck
check post# 10