Does it come with a warranty that is transferable to you since he never used the AC unit?
Seems fishy that he would just assume the AC compressor was blowing the 30 amp and order a new unit? Basic troubleshooting would have you shut down every RV component and start them individually to see where your problem lies.
Tom and Katharine
'07 Winnebago Tour 40TD, 400hp Cummins
'17 Winnebago View 24V, '02 R-Vision B+
RVing for 20 years & 200,000+ miles