1998 Minnie Winnie ceiling A/C not cold

The A/C on your roof is like a window unit, just a different shape. There are a few things like cleaning it, replacing starting capacitors or blower motors, some control boards, that can be done at reasonable cost, but the refrigeration unit is sealed and not meant to be serviced. Some shops that service RVs might be willing to tap a refrigerant line and add refrigerant, but what suggests that is underperformance reather than failure to cool. For getting into the core of the unit and trying to rebuild, shop time is often more expensive than a replacement, and it is hard to find a rebuilder.

RV dealer that does service can likely diagnose and figure out whether the problem is big or little. Expect to pay at least an hour of going shop rate to have it looked at.