Roof-mounted RV air conditioners under normal conditions work well and are relatively maintenance free. Owners can get into trouble when older units start to lose their cool.
While it may be tempting to attempt to recharge the freon on your RV’s A/C when it’s blowing warm air, you’re far better off having a professional address the issue.
One cause of RV air conditioner failure is damage caused by attempting to run it when plugged into an outlet not rated for a minimum of 30 amps. That reducer adapter that allows you to plug into your house receptacle can’t handle the load. The air conditioner will be running in a low voltage condition and burnout is very likely to happen.
Beyond replacing a damaged plastic shroud that covers the A/C, there is very little an RV owner should be doing in the way of repairs to an RV air conditioner.