Just another tip. Before you go running off to the dealership.
There is a 'DELAY' built in on the RV furnace and ac.
If you have been turning it "on and off and on and off". Its' cycling between delays and It will NEVER start.
It's not your house furnace! You are not giving it enough time.
The delay is very long on some RV's. Let it sit for an hour then turn it on and WAIT for the furnace to come on. It does seem like an eternity but wait it will come on.
My delay is so long that to this day 10 years later when I flip the ac on and when it doesn't come right on I still sometimes think oh my god it's broke.......then it turns on.
Albeit your dealership should have told you this but my guess is they didn't. :W Good luck I hope all goes well.