I have a 2019 19ERD Vista Cruiser and had the same problem. The sail switch is accessible from the outside furnace cover. The switch is in a holder and the holder is easier to remove than the sail switch itself. I pulled it out, flipped it back and forth several times, checked resistance with a multimeter to verify off and on and put it back. It works now. Some threads I read online talked about the switch being dirty, so maybe that was the problem. We took a trip a few weeks ago and the furnace worked flawlessly. Hope this helps.