Don't feel bad as we had the same issue too. Thanksgiving was our 2nd trip (first cold weather trip) in our new trailer and we are RV rookies. My wife finally figured it out on the 2nd night. I never would have known to do that and I'm not sure how she figured it out. Our trailer didn't come with a user manual for the furnace/AC systems. That first night sure was noisy and cold. Lol
Happy Camping!
Audra
2017 Freedom Express 257BHS
2004 F250 6.0L Powerstroke