Did you try switching the fan setting to low (most units have a hi or low option).
In S. Cal, it's unlikely you will run into icing as as that's generally an issue with high humidity. The moisture condenses on the fins (like the outside of a glass of ice water) but the fins are below freezing, so it then freezes...gradually it builds up until air can't flow between the fins and you get no air flow. Higher airflow helps avoid that issue. If you close off the vents, it creates a similar issue. If it does happen, just switch to fan only (no air/con) for 10-15min and it will quickly melt the ice.
Another question, do you actually have a ducted air/con? That would be unusual for a really small trailer. Usually the cold air just blows out of the main unit because you don't have to worry about getting cold air to a separate bedroom.
- If you do have a ducted unit, closing off just the vent blowing on your wife, shouldn't cause much issue.
- If it's blowing out of the main unit, you are probably cutting off 50% of the airflow if you close one side. That would be a bit of an issue if you are somewhere humid.
