Went through this when my brother visited in his RV and A/C quit on his. We went on line and did some basic research and ended up changing out his start capacitors that were originals. Also some wiring connections were a bit corroded and or loose. Believe we found the caps at auto parts store or maybe the local RV dealer,not sure. There are quite a few educational U-tube videos out there as well. Good luck!
Here's a couple sites that might get you headed in the right direction:
https://evapolar.com/blog/air-conditioner-does-not-keep-rv-cool/
https://www.fulltimefamilies.com/rv-ac-repair-guide/