Well check a few things first....have someone remove the cover and reach in with a hand and try to manually spin the blade...free spinning?....then tell the person below to click in the on postion while someone views from up top.....is it humming? or even trying to spin?....if not check the fuse on the RV that protects the A/C unit.....good?.....now replace the capacitor ( it the silver or gray can looking thing that the motor wires run to) only the correct size will work w/o causing further motor damage.

How to gain access to fan motor on brisk air 579 series roof mount air conditioner. thanks