I had exactly the same issue on my Tiffin RED Diesel pusher. No matter how low or high I moved that adjustment, I still froze over. At a Rally, the manufacturers visited coaches and in 2 seconds they said all they had to do was move that plastic piece from the outside fin to the third one in from the end. No more freezes.
You just pull that piece off the fin (towards the door). Make sure the wire thermistor (temperature probe) runs up the channel that hold the wire and reposition on that other fin.
Bob & Sue Rowan
2012 Coachmen Mirada 29DS (SOLD)
2015 Keystone Bullet Travel Trailer
2016 F-150 Lariat with Auto Trailer Backup
Dog = Morki (Yorkie-Maltese) - Zoe