Hey guys I may have something to add here. I have a 2022 Ram and it has been to the dealership 3 times to diagnose the no defrost issue. Specifically I demonstrated that when selecting front defrost only mode the air would blow out of the floor vents and only come out of the centre of the defrost vents. Didn't matter which speed the fan was or cycling through the other zones. Defrost wouldn't work properly.
I may have a solution or at least something to try. I noticed that SOMETIMES the defrost would work normally or at least it had intermittently worked, but I couldnt figure out what the common denominator was. But today I noticed it was working and the temperature was full hot. All air coming from the defrost and side window vents and nothing to the floor. I then lowered the temperature and noticed the air started coming out the floor vents!!
I have since determined, in my case anyways, that the full defrost mode will only work if at least one side of the temperature slider is full hot. Sync mode was the same. It would only go full defrost if the temperature is full hot.
I get why I couldn't get it to work other times is because usually it's in auto mode set at 21 degrees. And when switching to defrost mode I wouldn't normally change the temperature as well, It's usually blowing hot enough air in the winter. But it seemed to be consistent so far. Time will tell on more trips but it's the only thing that I've found to be repeatable and makes sense why I wouldn't have figured this out much sooner.
Put er on full hot and let me know if that doesn't do the trick.
Jason.